RPI SPI8

8-Channel SPI Bus Multiplexer for the Raspberry Pi

• 8 SPI channels
• Connects to the SPI pins on the Raspberry Pi
• Supports SPI star or daisy-chain topologies - or a mix of both
  • Daisy chain often used to get around the single Chip Select limitation (which this card fixes)
• 3.3V
  • 50 mA limit from Raspberry Pi

SPI Star Topology

• MISO from all slaves are wired together
• MOSI, SCLK is sent out to all ports
• SS (Slave Select) is separate for each of the 7 ports
• A0-A2 lines from Raspberry Pi control the port number

From Practical EE: SPI Bus page:

In Star topology all the signals are split and routed to each slave in parallel, except chip select. Multiple chip select are used to select individual slave devices. More devices support this mode than daisy-chain.

An example of a part (MCP4231 Digital Pot) which supports this mode (p 31):

SPI Daisy-Chain Topology

Daisy-chain mode could also be used via external wiring.

• MOSI / MISO from all slaves are connected in series
• SCLK is sent out to all ports
• Individual (Slave Select) is separate for each daisy-chain
• A0-A2 lines from Raspberry Pi control the port number

Connectors

40-Pin Raspberry Pi Connector

• SPIMISO - GPIO Pin 21
• SPIMOSI - GPIO Pin 19
• SPISCK - GPIO Pin 23
• SPICE0 - GPIO Pin 24
• Three GPIO pins select SPI channel
  • A0 - IO_22 - GPIO Pin 15
  • A1 - IO_27 - GPIO Pin 13
  • A2 - IO_17 - GPIO Pin 11

• BCM pin numbers

• PSOC5 to BCM mapping

SPI Connectors

Four of 2x6 right angle headers

1. SPICE0[0-7]
2. SPIMOSI
3. SPIMISO
4. SPISCK
5. VCC (3.3V from Raspberry Pi)
6. GND

Programming

• Set channel number on GPIO Pin 22 (A0), GPIO Pin 27 (A1), GPIO Pin 17 (A2)
• Do SPI transfer
• SPI on the Raspberry Pi
• Python Spidev

Application Example

Setup

• SPI0 is disabled by default.
  • To enable it, use raspi-config, or ensure the line dtparam=spi=on isn't commented out in /boot/config.txt.
  • By default it uses 2 chip select lines, but this can be reduced to 1 using dtoverlay=spi0-1cs.
  • dtoverlay=spi0-2cs also exists, and without any parameters it is equivalent to dtparam=spi=on.
• Use n SPI-POTX2 cards
• Requires n SPI cables

SPI Cables

RPI_SPI8 (Marking)	RPI_SPI8 Pin	SPI-POTX2 Pin	SPI-POTX2 Marking
Chip En (CE)	1	5	SS
MOSI (MO)	2	4	MOSI
MISO (MI)	3	1	MISO
SPICK (CK)	4	3	SCK
Vcc (+V)	5	2	+V
GND	6	6	GND

Timing

• RPI_PSOC5 Tester
• PSOC5 C code
• Yellow = center tap if POT0 (GND/VCC shunts installed
• Cyan = Slave Select/Chip Select

Factory Test Procedure

• Verifies continuity/No shorts or opens

Hardware Setup

• RPI_PSOC5
  • Raspberry Pi CPU Clone
• LED-TEST-2
  • Uses 11 LEDs
• POWER-49MM
  • Distribute grounds to LEDs
• Cable set
  • 2x6 header plugs into pair of SPI ports
  • 4 of 2x4 connectors attach to LED-TEST-2 card
    • (8) CE (SS)
    • MOSI
    • MISO
    • SCK

Run Tests

• Run puTTY
  • Find COM Port in Device Manager
  • 115,200 baud
  • RTS/CTS flow control

• Hit ENTER to see menu

Land Boards, LLC - RPi Card Test Station
1 - Select RPP-UIO-16 Card
2 - Select RPPSOC Card
3 - Select RASPI-PLUS-GVS-CFG Card
4 - Select RASPI-GVS Card
5 - Select RASPI-PLUS-GVS Card
6 - Select RPI-I2C-HUB Card
7 - Select RPI-SPI8 Card
R - Read EEPROM
W - Write EEPROM
B - Bounce LED across Card GPIOs
T - Test Card
D - Debug Card
? - Print this menu

• Select RPI-SPI8 Card by entering 7[ENTER]

7
Selected RPI-SPI8 card

Blink LEDs

• Enter B[ENTER]

B
Blinking the RPI-SPI8 Card LEDs, please wait

• Bounces LEDs off across the LEDs
  • 8 CE signals go low one at a time
  • MOSI, MISO, SCK cycles one on at time

Test Software

• Runs on RPI_PSOC5
• GitHub repo
  • Test_RPI_SPI8.c - Bounce LED across LED-TEST-2 card

Issues

Rev 1 Rework

• Cut etch between IC pins 5 and 6
• Add wire between IC pins 4 and 5

Assembly Sheet

RPI-SPI8 Assembly Sheet - Rev 1