Board Description¶

More detailed description of LimePSB RPCM board components and interconnections is given in the following sections of this chapter.

Raspberry CM4 Connector¶

LimePSB RPCM board is designed to use Raspberry Pi CM4 as a host computer. Raspberry Pi CM4L version without eMMC Flash memory is also supported. Board to board connectors (J1 and J2) are used to connect CM4 to the LimePSB RPCM board. Connector pinout, CM4 signals and schematic signal names are listed and described in Table 1.

Table 1. Raspberry Pi Compute Module connector pinout¶
CM4 Pin	CM4 reference	Schematic signal name	Description[1]
1	GND	GND	Ground (0V)
2	GND	GND	Ground (0V)
3	Ethernet_Pair3_P	ETH_TRD3_P	Ethernet pair 3 positive
4	Ethernet_Pair1_P	ETH_TRD1_P	Ethernet pair 1 positive
5	Ethernet_Pair3_N	ETH_TRD3_N	Ethernet pair 3 negative
6	Ethernet_Pair1_N	ETH_TRD1_N	Ethernet pair 1 negative
7	GND	GND	Ground (0V)
8	GND	GND	Ground (0V)
9	Ethernet_Pair2_N	ETH_TRD2_N	Ethernet pair 2 negative
10	Ethernet_Pair0_N	ETH_TRD0_N	Ethernet pair 0 negative
11	Ethernet_Pair2_P	ETH_TRD2_P	Ethernet pair 2 positive
12	Ethernet_Pair0_P	ETH_TRD0_P	Ethernet pair 0 positive
13	GND	GND	Ground (0V)
14	GND	GND	Ground (0V)
15	Ethernet_nLED3	ETH_LED_Y	Ethernet activity indicator
16	Ethernet_SYNC_IN	RPI_SYNC_IN_LS	IEEE1588 SYNC Input
17	Ethernet_nLED2	ETH_LED_G	Ethernet speed indicator
18	Ethernet_SYNC_OUT	RPI_SYNC_OUT_LS	IEEE1588 SYNC Output
19	Ethernet_nLED1	NC	Ethernet speed indicator
20	EEPROM_nWP	RPI_EEPROM_nWP	EEPROM write protect
21	Pi_nLED_Activity	RPI_STATUS_LED_G	Pi activity LED
22	GND	GND	Ground (0V)
23	GND	GND	Ground (0V)
24	GPIO26	PCIE_LED_WPAN	General purpose
25	GPIO21	RPI_SPI1_SCLK	General purpose
26	GPIO19	RPI_SPI1_MISO	General purpose
27	GPIO20	RPI_SPI1_MOSI	General purpose
28	GPIO13	RPI_PWM1	General purpose
29	GPIO16	PCIE_LED_WWAN	General purpose
30	GPIO6	RPI_RF_SW_TDD	General purpose
31	GPIO12	RPI_PWM0	General purpose
32	GND	GND	Ground (0V)
33	GND	GND	Ground (0V)
34	GPIO5	BUZZER	General purpose
35	ID_SC	RPI_ID_SC	BCM2711 GPIO 1
36	ID_SD	RPI_ID_SD	BCM2711 GPIO 0
37	GPIO7	RPI_SPI0_SS1	General purpose
38	GPIO11	RPI_SPI0_SCLK	General purpose
39	GPIO8	RPI_SPI0_SS0	General purpose
40	GPIO9	RPI_SPI0_MISO	General purpose
41	GPIO25	PCIE_LED_WLAN	General purpose
42	GND	GND	Ground (0V)
43	GND	GND	Ground (0V)
44	GPIO10	RPI_SPI0_MOSI	General purpose
45	GPIO24	RPI_BTN1	General purpose
46	GPIO22	RPI_GPIO22	General purpose
47	GPIO23	RPI_BTN2	General purpose
48	GPIO27	RPI_GPIO27	General purpose
49	GPIO18	RPI_SPI1_SS0	General purpose
50	GPIO17	RPI_SPI1_SS1	General purpose
51	GPIO15	RPI_UART0_RX	General purpose
52	GND	GND	Ground (0V)
53	GND	GND	Ground (0V)
54	GPIO4	RPI_GPIO4	General purpose
55	GPIO14	RPI_UART0_TX	General purpose
56	GPIO3	ADF_MUXOUT	General purpose
57	SD_CLK	RPI_SD_CLK	SD card clock signal
58	GPIO2	RPI_GPIO2	General purpose
59	GND	GND	Ground (0V)
60	GND	GND	Ground (0V)
61	SD_DAT3	RPI_SD_D3	SD card/eMMC Data3 signal
62	SD_CMD	RPI_SD_CMD	SD card/eMMC Command signal
63	SD_DAT0	RPI_SD_D0	SD card/eMMC Data0 signal
64	SD_DAT5	NC	SD card/eMMC Data5 signal
65	GND	GND	Ground (0V)
66	GND	GND	Ground (0V)
67	SD_DAT1	RPI_SD_D1	SD card/eMMC Data1 signal
68	SD_DAT4	NC	SD card/eMMC Data4 signal
69	SD_DAT2	RPI_SD_D2	SD card/eMMC Data2 signal
70	SD_DAT7	NC	SD card/eMMC Data7 signal
71	GND	GND	Ground (0V)
72	SD_DAT6	NC	SD card/eMMC Data6 signal
73	SD_VDD_Override	NC	Force SD card/eMMC interface
74	GND	GND	Ground (0V)
75	SD_PWR_ON	RPI_SD_PWR_ON	Output to power-switch for the SD card
76	Reserved	NC	Do not connect
77	+5V (Input)	VCC5P0	4.75V-5.25V. Main power input
78	GPIO_VREF	VCC3P3	GPIO reference voltage
79	+5V (Input)	VCC5P0	4.75V-5.25V. Main power input
80	SCL0	RPI_I2C0_SCL	I2C clock pin
81	+5V (Input)	VCC5P0	4.75V-5.25V. Main power input
82	SDA0	RPI_I2C0_SDA	I2C Data pin
83	+5V (Input)	VCC5P0	4.75V-5.25V. Main power input
84	CM4_3.3V (Output)	VCC3P3_RPI	3.3V ± 2.5%. Power Output
85	+5V (Input)	VCC5P0	4.75V-5.25V. Main power input
86	CM4_3.3V (Output)	VCC3P3_RPI	3.3V ± 2.5%. Power Output
87	+5V (Input)	VCC5P0	4.75V-5.25V. Main power input
88	CM4_1.8V (Output)	VCC1P8_RPI	1.8V ± 2.5%. Power Output
89	WL_nDisable	RPI_WL_nDISABLE	Wireless interface disable
90	CM4_1.8V (Output)	VCC1P8_RPI	1.8V ± 2.5%. Power Output
91	BT_nDisable	RPI_BT_nDISABLE	Bluetooth interface disable
92	RUN_PG	RPI_RUN_PG	CM4 CPU reset/power good
93	nRPIBOOT	RPI_nRPIBOOT	booting from an RPI server
94	AnalogIP1	RPI_AIP1	Analogue input
95	PI_LED_nPWR	RPI_LED_nPWR	Power On LED
96	AnalogIP0	RPI_AIP0	Analogue input
97	Camera_GPIO	CAM1_GPIO0	Used to shut down the camera
98	GND	GND	Ground (0V)
99	GLOBAL_EN	RPI_GLOBAL_EN	CM4 enable
100	nEXTRST	RPI_nEXTRST	Output. Driven low during reset
101	USB_OTG_ID	RPI_USB_OTG_ID	USB OTG Pin
102	PCIe_CLK_nREQ	RPI_PCIE_CLK_nREQ	PCIe clock request
103	USB_N	RPI_USB_D_N	USB D-
104	Reserved	NC	Do not connect
105	USB_P	RPI_USB_D_P	USB D+
106	Reserved	NC	Do not connect
107	GND	GND	Ground (0V)
108	GND	GND	Ground (0V)
109	PCIe_nRST	RPI_PCIE_nRST	PCIe reset
110	PCIe_CLK_P	RPI_PCIE_CLK_P	PCIe clock Out positive
111	VDAC_COMP	RPI_TVDAC	Video DAC output
112	PCIe_CLK_N	RPI_PCIE_CLK_N	PCIe clock Out negative
113	GND	GND	Ground (0V)
114	GND	GND	Ground (0V)
115	CAM1_D0_N	CAM1_D0_N	Input Camera1 D0 negative
116	PCIe_RX_P	RPI_PCIE_RX_P	Input PCIe GEN 2 RX positive
117	CAM1_D0_P	CAM1_D0_P	Input Camera1 D0 positive
118	PCIe_RX_N	RPI_PCIE_RX_N	Input PCIe GEN 2 RX negative
119	GND	GND	Ground (0V)
120	GND	GND	Ground (0V)
121	CAM1_D1_N	CAM1_D1_N	Input Camera1 D1 negative
122	PCIe_TX_P	RPI_PCIE_TX_P	Output PCIe GEN 2 TX positive
123	CAM1_D1_P	CAM1_D1_P	Input Camera1 D1 positive
124	PCIe_TX_N	RPI_PCIE_TX_N	Output PCIe GEN 2 TX positive
125	GND	GND	Ground (0V)
126	GND	GND	Ground (0V)
127	CAM1_C_N	CAM1_CLK_N	Input Camera1 clock negative
128	CAM0_D0_N	NC	Input Camera0 D0 negative
129	CAM1_C_P	CAM1_CLK_P	Input Camera1 clock positive
130	CAM0_D0_P	NC	Input Camera0 D0 positive
131	GND	GND	Ground (0V)
132	GND	GND	Ground (0V)
133	CAM1_D2_N	NC	Input Camera1 D2 negative
134	CAM0_D1_N	NC	Input Camera0 D1 negative
135	CAM1_D2_P	NC	Input Camera1 D2 positive
136	CAM0_D1_P	NC	Input Camera0 D1 positive
137	GND	GND	Ground (0V)
138	GND	GND	Ground (0V)
139	CAM1_D3_N	NC	Input Camera1 D3 negative
140	CAM0_C_N	NC	Input Camera0 clock negative
141	CAM1_D3_P	NC	Input Camera1 D3 positive
142	CAM0_C_P	NC	Input Camera0 clock positive
143	HDMI1_HOTPLUG	HDMI1_HOTPLUG	Input HDMI1 hotplug
144	GND	GND	Ground (0V)
145	HDMI1_SDA	HDMI1_SDA	A Bidirectional HDMI1 SDA
146	HDMI1_TX2_P	HDMI1_D2_P	Output HDMI1 TX2 positive
147	HDMI1_SCL	HDMI1_SCL	Bidirectional HDMI1 SCL
148	HDMI1_TX2_N	HDMI1_D2_N	Output HDMI1 TX2 negative
149	HDMI1_CEC	HDMI1_CEC	Input HDMI1 CEC
150	GND	GND	Ground (0V)
151	HDMI0_CEC	HDMI0_CEC	Input HDMI0 CEC
152	HDMI1_TX1_P	HDMI1_D1_P	Output HDMI1 TX1 positive
153	HDMI0_HOTPLUG	HDMI0_HOTPLUG	Input HDMI0 hotplug
154	HDMI1_TX1_N	HDMI1_D1_N	Output HDMI1 TX1 negative
155	GND	GND	Ground (0V)
156	GND	GND	Ground (0V)
157	DSI0_D0_N	NC	Output Display0 D0 negative
158	HDMI1_TX0_P	HDMI1_D0_P	Output HDMI1 TX0 positive
159	DSI0_D0_P	NC	Output Display0 D0 positive
160	HDMI1_TX0_N	HDMI1_D0_N	Output HDMI1 TX0 negative
161	GND	GND	Ground (0V)
162	GND	GND	Ground (0V)
163	DSI0_D1_N	NC	Output Display0 D1 negative
164	HDMI1_CLK_P	HDMI1_CLK_P	Output HDMI1 clock positive
165	DSI0_D1_P	NC	Output Display0 D1 positive
166	HDMI1_CLK_N	HDMI1_CLK_N	Output HDMI1 clock negative
167	GND	GND	Ground (0V)
168	GND	GND	Ground (0V)
169	DSI0_C_N	NC	Output Display0 clock negative
170	HDMI0_TX2_P	HDMI0_D2_P	Output HDMI0 TX2 positive
171	DSI0_C_P	NC	Output Display0 clock positive
172	HDMI0_TX2_N	HDMI0_D2_N	Output HDMI0 TX2 negative
173	GND	GND	Ground (0V)
174	GND	GND	Ground (0V)
175	DSI1_D0_N	DSI1_D0_N	Output Display1 D0 negative
176	HDMI0_TX1_P	HDMI0_D1_P	Output HDMI0 TX1 positive
177	DSI1_D0_P	DSI1_D0_P	Output Display1 D0 positive
178	HDMI0_TX1_N	HDMI0_D1_N	Output HDMI0 TX1 negative
179	GND	GND	Ground (0V)
180	GND	GND	Ground (0V)
181	DSI1_D1_N	DSI1_D1_N	Output Display1 D1 negative
182	HDMI0_TX0_P	HDMI0_D0_P	Output HDMI0 TX0 positive
183	DSI1_D1_P	DSI1_D1_P	Output Display1 D1 positive
184	HDMI0_TX0_N	HDMI0_D0_N	Output HDMI0 TX0 negative
185	GND	GND	Ground (0V)
186	GND	GND	Ground (0V)
187	DSI1_C_N	DSI1_CLK_N	Output Display1 clock negative
188	HDMI0_CLK_P	HDMI0_CLK_P	Output HDMI0 clock positive
189	DSI1_C_P	DSI1_CLK_P	Output Display1 clock positive
190	HDMI0_CLK_N	HDMI0_CLK_N	Output HDMI0 clock negative
191	GND	GND	Ground (0V)
192	GND	GND	Ground (0V)
193	DSI1_D2_N	NC	Output Display1 D2 negative
194	DSI1_D3_N	NC	Output Display1 D3 negative
195	DSI1_D2_P	NC	Output Display1 D2 positive
196	DSI1_D3_P	NC	Output Display1 D3 positive
197	GND	GND	Ground (0V)
198	GND	GND	Ground (0V)
199	HDMI0_SDA	HDMI0_SDA	Bidirectional HDMI0 SDA
200	HDMI0_SCL	HDMI0_SCL	Bidirectional HDMI0 SCL

Raspberry Pi CM4 Configuration Headers¶

LimePSB RPCM board has several headers dedicated for Raspberry Pi CM4 configuration, debug, analog inputs or other purposes. Header J14 (SYS) pins, schematic signal names and description are given in Table 2.

Table 2. SYS header pinout¶
Pin	Schematic signal name	Description
1	GND	Ground (0V)
2	RPI_nRPIBOOT	A low on this pin forces CM4 booting. To enable Raspberry Pi USB boot also place nRPIBOOT jumper on J14 pins 1-2. Place jumper on header J28 to switch Raspberry Pi USB from USB hub to USB C connector.
3	GND	Ground (0V)
4	RPI_EEPROM_nWP	CM4 on-board EEPROM write protect
5	RPI_AIP0	Analogue input
6	RPI_AIP1	Analogue input
7	GND	Ground (0V)
8	RPI_SYNC_IN	IEEE1588 SYNC Input
9	RPI_SYNC_OUT	IEEE1588 SYNC Output
10	GND	Ground (0V)
11	RPI_TVDAC	Video DAC output
12	GND	Ground (0V)
13	RPI_RUN_PG_BUFF	Buffered (5V output) RPI_RUN_PG line. High signal indicates CM4 CPU is running.
14	RPI_GLOBAL_EN	Drive low to power off CM4. A button between pins 13-14 can be used to wake up compute module from power down.

Description of additional control connector J5 (not fitted) for Raspberry Pi CM4 pinout is given in Table 3.

Table 3. Raspberry Pi CM4 J5 enable header¶
Pin	Schematic signal name	Description
1	RPI_GLOBAL_EN	Drive low to power off CM4.
2	GND	Ground (0V)
3	RPI_RUN_PG	Drive low to reset CM4 CPU/high signal indicates CM4 CPU is running.

Raspberry Pi Compute Module 4 on board WiFi and Bluetooth disable signals may be controlled by header J6 (not fitted) as shown in Table 4.

Table 4. Raspberry Pi CM4 J6 WiFi and Bluetooth control header pinout¶
Pin	Schematic signal name	Description
1	RPI_WL_nDISABLE	Drive low to disable wireless interface
2	GND	Ground (0V)
3	RPI_BT_nDISABLE	Drive low to reset CM4 CPU/high signal indicates CM4 CPU is running

Mini PCIe x1 Socket¶

LimePSB RPCM board features mini PCIe x1 specification compatible socket. LimePSB RPCM board mPCIe socket is also compatible with some non-standard expansion boards like LimeSDR XTRX, LoRaWAN and LoRa Core. More detailed information is listed in Table 5.

Table 5. LimePSB RPCM board Mini PCIe x1 connector pinout¶
Pin	Mini PCIe x1 Specification Reference	LimePSB RPCM schematic signal name	XTRX reference	LoRaWAN reference	SX1302/03 Corecell schematic signal name
1	Wake#	NC	Wake#	NC	NC
2	3.3 Vaux	VCC3P3	+3.3V	VCC	VCC5V_IN
3	COEX1	PCIE_COEX1	1PPSI_GPIO1(1N)	NC	NC
4	GND	GND	GND	GND	GND
5	COEX2	PCIE_COEX2	1PPSO_GPIO2(1P)	PPS_IN	NC
6	GND	VCC1P5	+1.5V	NC	GPIO(6) (NC)
7	CLKREQ#	RPI_PCIE_CLK_nREQ	CLKREQ#	NC	NC
8	UIM PWR	UIM_PWR	UIM_PWR	NC	NC
9	GND	GND	GND	GND	GND
10	UIM_DATA	UIM_DATA	UIM_DATA	SWDIO	NC
11	REFCLK-	RPI_PCIE_CLK_N	REF_CLK-	NC	NC
12	UIM_CLK	UIM_CLK	UIM_CLK	SWCLK	NC
13	REFCLK+	RPI_PCIE_CLK_P	REF_CLK+	NC	NC
14	UIM_RESET	UIM_RESET	UIM_RESET	NC	NC
15	GND	GND	GND	GND	GND
16	UIM_VPP	UIM_VPP	UIM_VPP	BOOT0	POWER_EN(NC)
17	Reserved	PCIE_UIM8	TDD_GPIO3_N	NC	HOST_SCK (NC)
18	GND	GND	GND	GND	GND
19	Reserved	PCIE_UIMC4	MHZ_IN	NC	HOST_MISO(NC)
20	W_DISABLE#	NC	TDD_GPIO3_P	nDISABLE	NC
21	GND	GND	GND	GND	GND
22	PERST#	RPI_PCIE_nRST	PERST#	nRESET	SX1302_RESET_HOST (NC)
23	PERn0	RPI_PCIE_RX_N	PERn0	NC	HOST_MOSI(NC)
24	3.3Vaux	VCC3P3	+3.3Vaux	VCC	SX1261_BUSY (NC)
25	PERp0	RPI_PCIE_RX_P	PERp0	NC	HOST_CSN (NC)
26	GND	GND	GND	GND	GND
27	GND	GND	GND	GND	GND
28	1.5Volt	VCC1P5	+1.5V	NC	SX1302_GPIO_8 (NC)
29	GND	GND	GND	GND	GND
30	SMB CLK	PCIE_SMB_CLK	MHZ_OUT	NC	I2C_SCL (NC)
31	PETn0	PCIE_PET0_N	PETn0	NC	PPS
32	SMB Data	PCIE_SMB_DATA	GPIO8	NC	I2C_SDA (NC)
33	PETp0	PCIE_PET0_P	PETp0	NC	NC
34	GND	GND	GND	GND	GND
35	GND	GND	GND	GND	GND
36	USB_D-	PCIE_USB_N	USB_DN	USB_D- / Tx	USB_DM
37	GND	GND	GND	GND	GND
38	USB_D+	PCIE_USB_P	USB_DP	USB_D+ / Rx	USB_DP
39	3.3Vaux	VCC3P3	PERp1	VCC	VCC3V3_IN
40	GND	GND	GND	GND	GND
41	3.3Vaux	VCC3P3	PERp1	VCC	VCC3V3_IN
42	LED_WWAN#	PCIE_LED_WWAN	LED_WWAN#_GPIO5	nTX	NC
43	GND	GND	GND	GND	GND
44	LED_WLAN#	PCIE_LED_WLAN	LED_WLAN#_GPIO6	nRX	SX1261_NSS (NC)
45	Reserved	NC	GND	NC	JTCK-SWCLK (NC)
46	LED_WPAN#	PCIE_LED_WPAN	LED_WPAN#_GPIO7	NC	SX1261_DIO1 (NC)
47	Reserved	NC	PETn1	NC	JTMS-SWDIO (NC)
48	1.5Volt	VCC1P5	+1.5V	NC	SX1261_NRESET(NC)
49	Reserved	NC	PETp1	NC	MCU_NRESET (NC)
50	GND	GND	GND	GND	GND
51	Reserved	NC	GND	NC	MCU_BOOT0 (NC)
52	3.3Vaux	VCC3P3	+3.3V	VCC	VCC3V3_IN

RF Front End¶

LimePSB RPCM RF path features power amplifiers, low noise amplifiers and SPDT switches as shown in Figure 1.

../_images/LimePSB-RPCM_v1.1_diagrams_r1_RFFE.png

Figure 1: LimePSB RPCM 1v1 RF path block diagram¶

A single control signal (RF_SW_TDD) is used to control all RF switches simultaneously for both A and B channels to change between TDD and FDD modes as shown in Table 6.

Table 6. RF path truth table¶
Control signal (RF_SW_TDD)	TRXA/B connected to	RXA/B connected to
Low	TXA/B_IN	RXA/B_OUT
High	RXA/B_OUT	NC

By default RF switches may be controlled from mPCIe expansion board pin 17 (via resistor R40). Optional control source may be RFFE TDD control header (J21) or CM4 GPIO6 (resistor R41 must be soldered).

RF path contains two types of connectors: board edge SMA connectors (J42, J43, J46, J47) used for external connections (antennas or cables) and U.FL connectors (J40, J41, J44, J45) used for internal connections (for example to connect to XTRX mini PCIe expansion board).

Signal frequency range of TX and RX paths are listed in Table 7.

Table 7. RF path signal frequency range¶
Direction	Frequency range
TX	100 MHz - 6 GHz
RX	100 MHz - 4 GHz

More detailed RF path component parameters are given in Table 8.

Table 8. RF path components parameters¶
Component	Function	Gain, dB	Output P1dB, dBm	NF, dB
SBB-5089	TX amplifier	20.5dB (850 MHz) 19.0dB (1950 MHz) 15.5dB (6000 MHz)	20.5dBm (850 MHz) 20.4dBm (1950 MHz) 14.7dBm (4000 MHz)	3.8dB (850 MHz) 4.1dB (1950 MHz) 4.6dB (4000 MHz)
SPF5043Z	RX amplifier	18.2dB (900 MHz) 12.9dB (1960 MHz) 7.0dB (3800 MHz)	22.6dBm (900 MHz) 22.7dBm (1900 MHz) 22.8dBm (3800 MHz)	0.8dB (900 MHz) 0.8dB (1900 MHz) 1.5dB (3800 MHz)
SKY13286	RF switch	-0.7dB (1000 MHz) -0.8dB (2000 MHz) -1.6dB (6000 MHz)	30.dBm (2000 MHz)

LimePSB RPCM RF front end uses same design as Front End Adapter. For more information about the design check LimeSDR XTRX documentation

USB Subsystem¶

LimePSB RPCM features USB2.0 hub, type-C, double type-A sockets and headers. The USB subsystem diagram is as shown in Figure 9.

../_images/LimePSB-RPCM_v1.1_diagrams_r1_USB.png

Figure 9. LimePSB RPCM 1v1 USB subsystem diagram¶

Main LimeSPB RPCM board USB subsystem components:

USB type-C socket (J27) is primarily used as LimeSPB RPCM one of power supply sources (for more information check Power Distribution section). To enable RPi USB boot mount nRPIBOOT jumper on J14 pins 1-2 and mount a jumper on header J28 to switch Raspberry Pi USB from USB hub to USB C (more information check section 2.2 Raspberry Pi CM4 Configuration Headers).

USB type-A dual sockets (J29) may be used to connect USB peripherals to the Raspberry Pi CM4.

USB2.0 hub USB2517 (IC19) USB 2.0 hub expands Raspberry Pi CM4 USB port to dual USB socket (J29), header (J31) and mPCIe (J3). For more information check Table 9.

Table 9. USB2.0 (IC19) Hub signals¶
Pin	Pin name	Function	Schematic signal name	Connector ID
59/58	USBUP_DP/ USBUP_DM	Root port	USB_HUB_D0_P/ USB_HUB_D0_N	Connected to CM4 USB via USB switch
2/1	USBDN1_DP/ USBDN1_DM	Downstream port	USB_HUB_D1_P/ USB_HUB_D1_N	J3 (mPCIe)
4/3	USBDN2_DP/ USBDN2_DM	Downstream port	USB_HUB_D2_P/ USB_HUB_D2_N	J29 (bottom)
7/6	USBDN3_DP/ USBDN3_DM	Downstream port	USB_HUB_D3_P/ USB_HUB_D3_N	J29 (top))
9/8	USBDN4_DP/ USBDN4_DM	Downstream port	USB_HUB_D4_P/ USB_HUB_D4_N	J31 (pins 5/3)
12/11	USBDN5_DP/ USBDN5_DM	Downstream port	USB_HUB_D5_P/ USB_HUB_D5_N	J31 (pins 6/4)
54/53	USBDN6_DP/ USBDN6_DM	Downstream port	NC	NC
56/55	USBDN7_DP/ USBDN7_DM	Downstream port	NC	NC

User Interface Components¶

LimePSB RPCM board features five dual colour (red and green (RG)) LEDs, one green indication LED and two Ethernet activity LEDs (yellow and green). All board LEDs are highlighted in Figure 2.

Figure 2: LimePSB RPCM 1v1 user interface components¶

Dual color LEDs (LED1-LED4) are connected to shift register (IC14). Their function may be programmed according to the user requirements. Dual color LED5 indicates Raspberry Pi status. Green LED6 indicates board power. These LEDs are mounted on the front side of the board.

Ethernet connector J9 has two LEDs: yellow and green. LEDs indicate wired network activity and speed.

Default function of LEDs and related information is listed in Table 10.

Table 10. Default LED behaviour¶
Board Reference	Schematic name	Shift register (IC14) pin	Description
LED1	RPI_LED1_R	Q0	User defined.
	RPI_LED1_G	Q1
LED2	RPI_LED2_R	Q2	User defined.
	RPI_LED2_G	Q3
LED3	RPI_LED3_R	Q4	User defined.
	RPI_LED3_G	Q5
LED4	RPI_LED4_R	Q6	User defined.
	RPI_LED4_G	Q7
LED5	RPI_STATUS_LED_R		Green is connected to CM4 PI_LED_nPWR (Power On) and red is connected to Pi_nLED_Activity (Activity).
LED5	RPI_STATUS_LED_G
LED6	VCC3P3		Board power. Connected to 3.3 V power rail
Ethernet connector J9 LEDs	ETH_LED_Y		Green is connected to Ethernet_nLED2 (Ethernet speed indicator: 1Gbit or 100Mbit Link) and yellow is connected to Ethernet_nLED3 (Ethernet activity indicator).
Ethernet connector J9 LEDs	ETH_LED_G

A user button BTN1 is mounted on the front side of the board and can be used for various purposes. The button is connected to Raspberry Pi CM4 GPIO24, has external pull up resistors and is hardware debounced.

SPI, I2C, UART Interfaces¶

LimePSB RPCM features multiple low speed interfaces like SPI (SPI0, SPI1), I2C, UART. LimePSB RPCM low speed interfaces signal names, I/O standards are listed in Table 11.

Table 11. Raspberry Pi CM4 interface pins¶
Interface	Schematic signal name	CM4 pin	I/O standard	Comment
SPI0	RPI_SPI0_SCLK	38 (GPIO11)	3.3V	Serial Clock (CM4 output)
	RPI_SPI0_MOSI	44 (GPIO10)	3.3V	Data (CM4 output)
	RPI_SPI0_MISO	40 (GPIO9)	3.3V	Data (CM4 input)
	RPI_SPI0_SS0	39 (GPIO8)	3.3V	IC27 and IC29 DACs SPI slave select (CM4 output)
	RPI_SPI0_SS1	37 (GPIO7)	3.3V	IC28 phase detector SPI slave select (CM4 output)
SPI1	RPI_SPI1_SCLK	25 (GPIO21)	3.3V	Serial Clock (CM4 output)
	RPI_SPI1_MOSI	27 (GPIO20)	3.3V	Data (CM4 output)
	RPI_SPI1_MISO	26 (GPIO19)	3.3V	Data (CM4 input)
	RPI_SPI1_SS0	49 (GPIO18)	3.3V	IC8 ADC SPI slave select (CM4 output)
	RPI_SPI1_SS1	50 (GPIO17)	3.3V	IC14 AND IC16 Shift registers SPI slave select (CM4 output)
I2C0	RPI_I2C0_SCL	80	3.3V	Serial Clock (CM4 output)
I2C0	RPI_I2C0_SDA	82	3.3V	Data
UART0	RPI_UART0_RX	51 (GPIO15)	3.3V	Data (CM4 input)
UART0	RPI_UART0_TX	55 (GPIO14)	3.3V	Data (CM4 output)

RPI_I2C0 interface devices, addresses and other info are shown in Table 12.

Table 12. RPI_I2C0 interface devices¶
RPI_I2C0 slave device	Slave device	I2C address	I/O standard	Comment
IC9	Temperature sensor	1 0 0 1 0 0 0 RW	3.3V	LM75
IC10(default)/IC11	EEPROM	1 0 1 0 0 0 0 RW	3.3V	CAT24C128WI-GT3/M24128
IC12/IC13	secure key storage	1 1 0 0 0 0 0 RW	3.3V	ATECC508A
IC15/IC17	RTC	1 0 1 0 0 0 1 RW	3.3V	PCF85063AT
IC44	USB PD controller	0 0 0 1 0 0 0 RW	3.3V	CYPD3177-24LQXQT

Front Display Connector¶

LimePSB RPCM board has 5-pin 0.1” pitch header J8 with friction lock (Molex 0022112052 [7]). It is dedicated for front display connection. Front display connector J8 contains signals for I2C interface, button and power rail. More detailed information about the front display connector is provided inTable 13.

Table 13. Front screen connector (J8) pinout¶
J8 pin	Schematic signal name	Description
1	GND	Ground (0V)
2	VCC3P3	Power 3.3V (default) or 5V
3	RPI_ID_SD	I2C data
4	RPI_ID_SC	I2C clock
5	RPI_BTN2	User button 2 (debounced)

MIPI DSI Display and CSI Camera Connectors¶

LimePSB RPCM has two 15-pin FPC connectors for MIPI DSI display and MIPI CSI camera. MIPI DSI interface is used for connecting serial display. Detailed display 1 connector J17 pinout is as shown in Table 14.

Table 14. MIPI DSI Display 1 connector (J17) pinout¶
Pin	Schematic signal name	Description
1	GND	Ground (0V)
2	DSI1_D1_N	Output Display1 D1 negative
3	DSI1_D1_P	Output Display1 D1 positive
4	GND	Ground (0V)
5	DSI1_CLK_N	Output Display1 clock negative
6	DSI1_CLK_P	Output Display1 clock positive
7	GND	Ground (0V)
8	DSI1_D0_N	Output Display1 D2 negative
9	DSI1_D0_P	Output Display1 D2 positive
10	GND	Ground (0V)
11	RPI_I2C0_SCL	I2C clock
12	RPI_I2C0_SDA	I2C data
13	GND	Ground (0V)
14	VCC3P3	3.3V power rail
15	VCC3P3	3.3V power rail

MIPI CSI interface is used for serial camera. Detail camera 1 connector J18 pinout is as shown in Table 15.

Table 15. MIPI CSI Camera 1 connector pinout¶
Pin	Schematic signal name	Description
1	GND	Ground (0V)
2	CAM1_D0_N	Input Camera1 D0 negative
3	CAM1_D0_P	Input Camera1 D0 positive
4	GND	Ground (0V)
5	CAM1_D1_N	Input Camera1 D1 negative
6	CAM1_D1_P	Input Camera1 D1 positive
7	GND	Ground (0V)
8	CAM1_CLK_N	Input Camera1 clock negative
9	CAM1_CLK_P	Input Camera1 clock positive
10	GND	Ground (0V)
11	CAM1_GPIO0	Typically used to shut down the camera
12	CAM1_GPIO1	NC
13	RPI_I2C0_SCL	I2C clock
14	RPI_I2C0_SDA	I2C data
15	VCC3P3	3.3V power rail

HMDI, Ethernet Connectors and uSD Socket¶

LimePSB RPCM board features 2 vertically mounted full-size HDMI 2.0 connectors (J12 and J13). Data signals are directly connected between Raspberry Pi CM4 TMDS interfaces and HDMI connectors. 5V power for HDMI connectors is supplied via a current-limited switch (IC7).

LimePSB RPCM board also features Gigabit Ethernet and power over Ethernet (PoE) capable RJ45 connector (J9).

For Raspberry Pi CM4L module (Raspberry Pi CM4 without eMMC Flash memory) microSD card push-push socket (J7) must be used along with the appropriate uSD card.

GPIO Connector¶

Some Raspberry Pi Compute Module 4 GPIOs are connected to 20 pin 0.1” J10 header. Three pins of this connector are dedicated for power (3.3 V and 5V). GPIO header pins (J10) and additional information is given in Table 16.

Table 16. Raspberry Pi CM4 GPIO header (J10) pins¶
Connector pin	Schematic signal name	CM4 pin	I/O standard	Comment
1	VCC3P3		3.3V	3.3V power rail
2	VCC5P0		5.0V	5.0V power rail
3	RPI_GPIO22	GPIO22	3.3V	General purpose
4	VCC5P0		5.0V	5.0V power rail
5	RPI_GPIO27	GPIO27	3.3V	General purpose
6	GND			Ground (0V)
7	GND			Ground (0V)
8	RPI_UART0_TX	GPIO14	3.3V	General purpose configured as UART output
9	RPI_SPI0_MOSI	GPIO10	3.3V	General purpose configured as SPI output
10	RPI_UART0_RX	GPIO15	3.3V	General purpose configured as UART input
11	RPI_SPI0_MISO	GPIO9	3.3V	General purpose configured as SPI input
12	GND			Ground (0V)
13	RPI_SPI0_SCLK	GPIO11	3.3V	General purpose configured as SPI clock
14	GND			Ground (0V)
15	RPI_GPIO2	GPIO2	3.3V	General purpose
16	RPI_GPIO4	GPIO4	3.3V	General purpose
17	RPI_ID_SD	ID_SD	3.3V	General purpose
18	RPI_ID_SC	ID_SC	3.3V	General purpose
19	GND			Ground (0V)
20	GND			Ground (0V)

Board Temperature Control¶

LimePSB RPCM board has two dedicated 0.1” pitch headers J25 and J26 for fans. Header J25 is standard 4-pin fan header while J25 is 2-pin header. Fan control voltage is 5V by default, but it may be changed to 3.3V or supply voltage VCC_INT by resistors. Fan power may be controlled from shift register IC16 output Q7 (FAN_CTRL, default) or directly from temperature sensor IC9 pin 3 (LM75_OS).

Clock Distribution¶

LimePSB RPCM board clock network comprises of on-board voltage controlled crystal oscillators, phase detector, clock buffer, reference clock input and output connectors and clock source selection pin headers. Board clock distribution block diagram is as shown in Figure 3.

../_images/LimePSB-RPCM_v1.1_diagrams_r1_clock.png

Figure 3. LimePSB RPCM 1v1 board clock distribution block diagram¶

LimePSB RPCM board distributes reference clock to and from Raspberry Pi Compute Module 4, mini PCIe connector and external sources. It is possible to connect external reference clock and PPS signals to and from another boards or systems via J32 (EXT_SYNC_IN) and J35 (EXT_SYNC_OUT) connectors. Clock path may be configured using jumpers and resistors as described in Table 17.

Table 17. LimePSB RPCM clock signal selection¶
Schematic ID	Input signal	Output signal	Description
J36	EXT_SYNC_IN	REF_CLK_IN	Phase detector (IC28) input selection
J36	RPI_SYNC_OUT	REF_CLK_IN	Phase detector (IC28) input selection
J37	RPI_SYNC_OUT	PCIE_PPS_IN	PPS signal source selection for mPCIe expansion boards
J37	EXT_SYNC_IN	PCIE_PPS_IN	PPS signal source selection for mPCIe expansion boards
J38	EXT_SYNC_IN	RPI_SYNC_IN	CM4 SYNC_IN synchronization input source selection
J38	PCIE_PPS_OUT	RPI_SYNC_IN	CM4 SYNC_IN synchronization input source selection
J39	EXT_SYNC_IN	PCIE_UIMC4	Reference clock selection for mPCIE exanpsion board (XTRX)
J39	LMK_CLK_OUT2	PCIE_UIMC4	Reference clock selection for mPCIE exanpsion board (XTRX)
J34	RPI_SYNC_OUT	EXT_SYNC_OUT	Synchronization output signal selection
	PCIE_PPS_OUT
	LMK_CLK_OUT3
R141	PCIE_PPS_IN	PCIE_COEX1	PPS signal output for mPCIE expansion board (XTRX)
R3	PCIE_PPS_IN	PCIE_PETn0	PPS signal output for mPCIE expansion board (LoRa Semtech)
R1	PCIE_PPS_IN	PCIE_COEX2	PPS signal output for mPCIE expansion board (LoRa n-Fuse) and PPS output for (XTRX)
R2	PCIE_COEX2	PCIE_PPS_OUT	PPS signal input from mPCIE expansion board (XTRX)
R6	PCIE_SMB_CLK	PCIE_PPS_OUT	Clock signal input from mPCIE expansion board (XTRX)

LimePSB RPCM board has several on-board crystal oscillator (XO) options that may be used as source for clock buffer LMK00101. By default voltage controlled oven compensated crystal oscillator (VCOCXO) XO1 is populated. Optional voltage controlled temperature compensated crystal oscillators XO2 – XO5 (VCTCXO) are not populated by default. All these XOs may be tuned by DAC (16-bit IC27 default or 8-bit IC29) or phase detector (IC28).

Clock network components are listed in Table 18.

Table 18. LimePSB RPCM clock distribution system components¶
Designator	Type	Part number	Description	Description
XO1	VCOCXO	U7475LF 30.72MHz	30.72 MHz
XO2	VCTCXO	E6245LF 30.72 MHz	30.72 MHz	Not mounted
XO3		E5280LF 30.72MHz	30.72 MHz	Not mounted
XO4		RTX5032A, 40.00MHz	40 MHz	Not mounted
XO5		ASVTX-12-A-38.400MHZ-H10-T	38.4 MHz	Not mounted
IC27	DAC	AD5662	16 Bit
IC29	DAC	AD5601BKSZ-REEL7	8 Bit	Not mounted
IC25	Clock buffer	LMK00105SQ/NOPB
IC28	Phase detector	ADF4002BCPZ-RL7

Power Distribution¶

LimePSB RPCM board power delivery network consists of different power rails with different regulators, voltages and filters. LimePSB RPCM board power distribution block diagram is presented in Figure 4.

../_images/LimePSB-RPCM_v1.1_diagrams_r1_power.png

Figure 4. LimePSB RPCM 1v1 board power distribution block diagram¶

LimePSB RPCM board may be supplied from USB Type-C port (USB Power delivery), Ethernet RJ45 port (PoE) or barrel DC connector (9-14V):

USB Type-C socket (9-12V 2.5 A or 1.5 A) may be used to supply LimePSB-RPCM board. In this case make sure that USB Power Delivery 18W or more power adapter is used. Depending on application board requested current from source may be lowered from 2.5A to 1.5A by placing jumper on header J48.

RJ45 socket is an alternative way to supply the LimePSB RPCM board. Make sure PoE+ (802.3at) class 4 compliant power source is used.

Barrel connector (9-14V 2A) also may be used to power LimePSB RPCM board.

To keep RTC running when board power is disconnected 3V CR1220 battery must be inserted into BATT1 battery holder.