Sharing SPI Adafruit PiTFT and RFID RC522

Question

I have a Pi Zero 1.2 connected to an Adafruit 2.8" PiFTF screen and a RFID-RC522 board. I also have a thermal printer connected to TX/RX, but I don't think this plays a part in my question.

The TFT screen has a 26 pin header, designed for the older Pi boards. It also has a breakout connector underneath giving access to these same pins.

The RFID board is connected as per the instructions here: https://github.com/ondryaso/pi-rc522

The problem

My problem is that I can either have the TFT screen working, or the RFID, but not both at the same time. At the moment I have commented out this line in /boot/config.txt to work on the RFID:

#dtoverlay=pitft28-capacitive,rotate=270,speed=64000000,fps=30

I'm a bit stuck trying to figure out if it's possible to have both the TFT and the RFID connected and working. I understand there may be an alternative way to connect the RFID to a second SPI SPI1?

What have I tried?

I have enabled dtoverlay=spi1-1cs in /boot/config.txt and can see the following:

crw-rw---- 1 root spi 153, 0 Aug  2 19:01 spidev0.1
crw-rw---- 1 root spi 153, 1 Aug  2 19:01 spidev1.0

But when I run my RFIDUtil.py (from ondryaso GitHub), it errors out with:

$ sudo python rfid-util.py 
Traceback (most recent call last):
  File "rfid-util.py", line 5, in <module>
    rdr = RFID()
  File "/home/pi/Development/printer/rfid/pirc522/rfid.py", line 68, in __init__
    self.spi.open(bus, device)
IOError: [Errno 2] No such file or directory

The code is as follows:

from pirc522 import RFID
import signal
import time

rdr = RFID()
util = rdr.util()
# Set util debug to true - it will print what's going on
util.debug = True

while True:
    # Wait for tag
    rdr.wait_for_tag()

    # Request tag
    (error, data) = rdr.request()
    if not error:
        print("\nDetected")

        (error, uid) = rdr.anticoll()
        if not error:
            # Print UID
            print("Card read UID: "+str(uid[0])+","+str(uid[1])+","+str(uid[2])+","+str(uid[3]))

            # Set tag as used in util. This will call RFID.select_tag(uid)
            util.set_tag(uid)
            # Save authorization info (key B) to util. It doesn't call RFID.card_auth(), that's called when needed
            util.auth(rdr.auth_b, [0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF])
            # Print contents of block 4 in format "S1B0: [contents in decimal]". RFID.card_auth() will be called now
            util.read_out(4)
            # Print it again - now auth won't be called, because it doesn't have to be
            util.read_out(4)
            # Print contents of different block - S1B2 - RFID.card_auth() will be called again
            util.read_out(6)
            # We can change authorization info if you have different key in other sector
            util.auth(rdr.auth_a, [0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF])
            #If you want to use methods from RFID itself, you can use this for authorization
            # This will authorize for block 1 of sector 2 -> block 9
            # This is once more called only if it's not already authorized for this block
            util.do_auth(util.block_addr(2, 1))
            # Now we can do some "lower-level" stuff with block 9
            rdr.write(9, [0x01, 0x23, 0x45, 0x67, 0x89, 0x98, 0x76, 0x54, 0x32, 0x10, 0x69, 0x27, 0x46, 0x66, 0x66, 0x64])
            # We can rewrite specific bytes in block using this method. None means "don't change this byte"
            # Note that this won't do authorization, because we've already called do_auth for block 9
            util.rewrite(9, [None, None, 0xAB, 0xCD, 0xEF])
            # This will write S2B1: [0x01, 0x23, 0xAB, 0xCD, 0xEF, 0x98, 0x76......] because we've rewritten third, fourth and fifth byte
            util.read_out(9)
            # Let's see what do we have in whole tag
            util.dump()
            # We must stop crypto
            util.deauth()

These questions are similar, but haven't got me a working solution as yet.

• How to enable SPI1 and SPI0 at the same time?
• How to enable spi1? / pi 3 and two rc522 RFID readers
• How to connect 2 RFID readers (RC522)

I have access to PiZero 1.3 and PiZero W if that makes any difference? Any help greatly appreciated.

Answer 1

Using the answers from Dirk, I have got both my 2.8" TFT and RFID-RC522 working.

I have set dtoverlay=spi1-1cs in /boot/config.txt giving me:

$ ls /dev/spi*
/dev/spidev0.0
/dev/spidev0.1

I connected the TFT as normal and then assigned the RFID pins as follows:

RFID    Pi Pin  Pin Name
SDA     37      GPIO26 (dtparam sets this as CE0)
SCK     40      SPI1 SCLK
MOSI    38      SPI1 MOSI
MISO    35      SPI1 MISO
IRQ     29      GPIO5
GND     39      Ground
RST     31      GPIO6
3.3V    17      VDD_3V3

I then called the RFID class

def __init__(self, bus=0, device=0, speed=1000000, pin_rst=def_pin_rst,
            pin_ce=0, pin_irq=def_pin_irq, pin_mode = def_pin_mode):

Using this modified line in my code:

rdr = RFID(1, 0, 1000000, 31, 37, 29)

This now shows the TFT screen and lets me use the RFID.