581 Register bank accessible through SPI and I2C :: Quicker, easier and cheaper to make your own chip!

How it works

Register bank accessible throught two different serial interfaces: SPI and I2C. Use digital input to select prefered interface.

There are 8 read/write 8 bit registers and 8 read only 8 bit registers.

Address 0 (first byte in read/write register space) drives the 7 segment display.

Digital input ui_in[7] = 0 selects SPI and ui_in[7] = 1 selects I2C.

SPI peripheral design based on https://github.com/calonso88/tt07_alu_74181

See that design's docs for information about the SPI peripheral.

Small improvement done on the spi_peripheral module. There used to be two buffer counters (one for RX and one for TX). Since the counters are not used together, it was possible to remove one of them and use a single buffer counter. This has reduced 4 flip flops in total and some combinatorial logic as well.

Added logic to control driver for MISO. On previous submissions of this design, the MISO was always driven. Logic has been added to put MISO into high impedance when CS_N is driven high. Due to a 2-stage synchronizer, the MISO goes to high impedance after 2 clock cycles.

I2C peripheral design based on https://github.com/sanojn/tt06_ttrpg_dice

See that design's docs for information about the I2C peripheral.

How to test

Use SPI1 Master peripheral in RP2040 to start communication on SPI interface towards this design. Remember to configure the SPI mode using the switches in DIP switch (if you'd like to have CPOL=1 and CPHA=1). Alternatively, don't use the DIP switches and use the RP2040 GPIOs to configure the SPI mode in the desired mode.

Example code to initialize SPI in REPL:

spi_miso = tt.pins.pin_uio3
spi_cs = tt.pins.pin_uio4
spi_clk = tt.pins.pin_uio5
spi_mosi = tt.pins.pin_uio6
spi_miso.init(spi_miso.IN, spi_miso.PULL_DOWN)
spi_cs.init(spi_cs.OUT)
spi_clk.init(spi_clk.OUT)
spi_mosi.init(spi_mosi.OUT)
spi = machine.SoftSPI(baudrate=10000, polarity=0, phase=0, bits=8, firstbit=machine.SPI.MSB, sck=spi_clk, mosi=spi_mosi, miso=spi_miso)
spi_cs(1)

Example code to write 0xF8 to address[0]:

spi_cs(0); spi.write(b'\x80\xF8'); spi_cs(1)

This should set the 7 segment LED to 0xF8 which will display "t."

Seg A - OFF, Seg B - OFF, Seg C - OFF, Seg D - ON, Seg E - ON, Seg F - ON, Seg G - ON, Seg DP - ON

Example code to read from address[0]:

spi_cs(0); spi.write(b'\x00'); spi.read(1); spi_cs(1)

The result should be 0xF8 or whatever you wrote to address[0].

TODO: I2C documentation.

External hardware

Not required. Write to the first register to set the LEDs on the demoboard.

External hardware

None.

#	Input	Output	Bidirectional
0	cpol	spare[0]
1	cpha	spare[1]	i2c_sda
2		spare[2]	i2c_scl
3		spare[3]	spi_miso
4		spare[4]	spi_cs_n
5		spare[5]	spi_clk
6	sel[1]	spare[6]	spi_mosi
7	sel[0]	spare[7]

581 Register bank accessible through SPI and I2C