Uart and Peripheral Pin Select

[peterverkaik]

Here is a test program to use Uart1 module to create 4 uart channels.
The mcu used is dsPIC33FJ128GP802/804

Code: Select all

program Uart_test

const
  RP0 = 0
  RP1 = 1
  RP2 = 2
  RP3 = 3
  RP4 = 4
  RP5 = 5
  RP6 = 6
  RP7 = 7

const Uart1TxPins as word[4] = (RP0,RP2,RP4,RP6)
const Uart1RxPins as word[4] = (RP1,RP3,RP5,RP7)
const Uart1Baud as word[4] = (9600,1200,19200,4800)

dim Uart1rxBuf as byte[256]
dim Uart1rxHead, Uart1rxTail as byte

dim hwUartChannel as word 'ch0=RP0,RP1 ch1=RP2,RP3 ch2=RP4,RP5 ch3=RP6,RP7

sub procedure Uart1rxInt org IVT_ADDR_U1RXINTERRUPT
  Uart1rxBuf[Uart1rxHead] = Uart1_Read()  'put char in buf
  Uart1rxHead = Uart1rxHead + 1           'increment head pointer
  IFS0.U1RXIF = 0                         'clear U1RXIF
end sub

sub procedure Uart1_Stop()
  IEC0.U1RXIE = 0 'disable U1RX interrupt
  U1MODE.UARTEN = 0 'disable uart1 module
end sub

main:
  ADPCFG = $FFFF  'In order to use PORTB pins for digital I/O, the corresponding bits in
                  'the ADPCFG register must be set to ‘1’, even if A/D module is turned off.

  'goal is to use uart1 module to support 4 uart channels
  'by remapping uart1 module to different pins in a roundrobin scheme
  while true
    LATB = LATB OR $00FF 'set latches to uart idle level
    TRISB = (TRISB AND $FF55) OR $0055 'make RP0,RP2,RP4,RP6 output, RP1,RP3,RP5,RP7 input
    for hwUartChannel = 0 to 3
      Unlock_IOLOCK()
      PPS_Mapping(Uart1RxPins[hwUartChannel],_INPUT,_U1RX)
      PPS_Mapping(Uart1TxPins[hwUartChannel],_OUTPUT,_U1TX)
      Lock_IOLOCK()
      Uart1rxHead = 0
      Uart1rxTail = 0
      Uart1_Init(Uart1Baud[hwUartChannel])
      Uart_Set_Active(@UART1_Read, @UART1_Write, @UART1_Data_Ready, @UART1_Tx_Idle)
      IPC2.U1RXIP_0 = 0 'U1RX interrupt priority 4
      IPC2.U1RXIP_1 = 0
      IPC2.U1RXIP_2 = 1
      IEC0.U1RXIE = 1 'enable U1RX interrupt
      'Send command
      Uart1_Write(0x41 + hwUartChannel) 'send 'A', 'B', 'C' or 'D'
      'Wait for response
      while Uart1rxTail = Uart1rxHead
      wend
      'Get response and echo
      Uart1_write(Uart1rxBuf[Uart1rxTail]) 'echo received bytes
      Uart1rxTail = Uart1rxTail + 1
      'Wait for transmission complete
      while Uart1_Tx_Idle = 0
      wend
      Uart1_Stop() 'disable uart1 module
      Delay_ms(2000) 'wait 2 seconds
    next hwUartChannel
  wend
end.

As the Uart library does not provide a Stop function, I declared
one myself.
Questions:

Do I take the right steps regarding unlock and lock functions?

Do I need to remap pins to _NULL before switching to next channel?
(I want a stopped channel to have its output pin at idle level)

Why is there no _NULL function for input pins?
(If I remap _U1RX it may be _U1RX is mapped to multiple pins)

regards peter

[jpc]

Peter,

peripheral inputs can be connected to only 1 pin at a time , however you can connect as many output-pins to a peripheral output as you want simultaneously e.g you could have the uart output connected to a number of pins and these will all behave identical.
Your mapping sequence seems ok btw, if you want to remap make sure the IOKOCK_Enable is cleared in the configuration settings.
If you want 4 uarts you better use one of the chips with 4 uarts ( e.g. p24FJ256GB110 family) instead of the multiplexing as you try to do, this will not work any better than simply using a rs485 buswhich has the advantage of allowing many nodes.

[peterverkaik]

peripheral inputs can be connected to only 1 pin at a time

Does this mean if I remap U1RX from RP1 to RP3, that RP1 comes
under control of LAT, TRIS and PORT automatically?

however you can connect as many output-pins to a peripheral output as you want simultaneously e.g you could have the uart output connected to a number of pins and these will all behave identical.

If I remap U1TX from RP0 to RP2 then I want RP0 to stay at idle
level, that's why I set LAT to 1 prior to using remapping. I assume
I must remap RP0 to NULL and then remap U1TX to RP2.

Thanks for the tip on IOLOCK_enable.
If this multiplexing works I may want to multiplex 8 uarts.
Also. the 802 comes in a relative small dip package.

regards peter

[jpc]

yes, you will have to disconnect the TX and yes, if you remap the RX the input's you mapped it to before should be released( allthough i must admit i never tested this)
I still think you waste energy on this multiplexing thing, this will never perform like 8 uarts, actually not even like 2. Well designed uart ISR's will capture any character as long as the buffers can hold it, multiplexing will introduce uart-errors allmost for sure unless you go for a master-slave protocol but this could be done with less effort on aRS485 bus which was designed for the purpose.

regards jpc