RPI SPI8

8-Channel SPI Bus Multiplexer for the Raspberry Pi

• 8 channels
• Supports SPI star topology
  • MISO from all slaves are wired together
• Connects to the SPI pins on the Raspberry Pi
• 3.3V
  • 50 mA limit from Raspberry Pi

SPI Star Topology

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):

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
  • GPIO Pin 22 - A0
  • GPIO Pin 27 - A1
  • GPIO Pin 17 - A2

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

Factory Test Procedure

• RPI_PSOC5 - Raspberry Pi Clone
• Verifies continuity/No shorts or opens
• LED-TEST-2
• POWER-49MM
  • Distribute grounds to LEDs
• Cables 2 ports at a time
  • 2x6 header plugs into pair of SPI ports
  • 4 of 2x4 connectors attach to LED-TEST-2 card
    • Power/Ground LED
    • MOSI
    • MISO
    • CE (SS)
    • SCK
• Bounces LEDs across the LEDs

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