Re^5: How to read serial port with WIN32:SerialPort?

in reply to Re^4: How to read serial port with WIN32:SerialPort?
in thread How to read serial port with WIN32:SerialPort?

The MAX3140 datasheet description of 9bit mode:

The MAX3140 supports a common multidrop communication  technique  refe
+rred  to  as  9-bit  mode.  In  this mode,  the  parity  bit  is  set
+  to  indicate  a  message  that  contains  a  header  with  a  desti
+nation  address.  Set  the MAX3140’s  parity  mask  to  generate  int
+errupts  for  this condition.  Operating  a  network  in  this  mode 
+ reduces the  processing  overhead  of  all  nodes  by  enabling  the
+ slave  controllers  to  ignore  most  message  traffic.  This reliev
+es  the  remote  processor  to  handle  more  useful tasks.In  9-bit 
+ mode,  the  MAX3140  is  set  up  with  eight  bits plus  parity.  T
+he  parity  bit  in  all  normal  messages  is clear,  but  is  set  
+in  an  address-type  message.  The MAX3140’s parity-interrupt mask g
+enerates an interrupton  high  parity  when  enabled.  When  the  mas
+ter  sends an address message with the parity bit set, all MAX3140  n
+odes  issue  an  interrupt.  All  nodes  then retrieve the received b
+yte to compare to their assigned address.  Once  addressed,  the  nod
+e  continues  to process each received byte. If the node was not addr
+essed,  it  ignores  all  message  traffic  until  a  new address is 
+sent out by the master.The parity/9th-bit interrupt is controlled onl
+y by the data in the receive register and is not affected by data in 
+the FIFO,  so  the  most  effective  use  of  the  parity/9th-bitinte
+rrupt is with FIFO disabled. With the FIFO disabled, received  non-ad
+dress  words  are  ignored  and  not  even read from the UART.
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The parity bit that this is referring to is a bit in an on-chip transmit control register. This register has to be modified to cause the chip generated parity bit to be set to indicate an address byte. And then be modified again to turn off address-mode.

My guess is the Device::SerialPort module doesn't use it's parity argument for this purpose.

James

There's never enough time to do it right, but always enough time to do it over...

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Re^6: How to read serial port with WIN32:SerialPort? by afoken (Chancellor) on Apr 15, 2021 at 06:22 UTC
The parity bit that this is referring to is a bit in an on-chip transmit control register. This register has to be modified to cause the chip generated parity bit to be set to indicate an address byte. And then be modified again to turn off address-mode. My guess is the Device::SerialPort module doesn't use it's parity argument for this purpose. Of course it does not. It becomes obvious when you read the POD of Device::SerialPort: parity One of the following: "none", "odd", "even". To use the parity bit for non-parity purposes, you would need other values, e.g. "mark" and "space" or simply "0" and "1". Also, `parity()` is one of the configuration parameter methods, not an operating method. It is not clear if changing the parity at operation time is supported: Some individual parameters (eg. baudrate) can be changed after the initialization is completed. These will be validated and will update the serial driver as required. Just to see an alternative implementation of a non-PC USART, here is a part of the documentation for the SERCOM peripheral of the Atmel/Microchip SAM D21 in USART Mode. It is also available in other SAMs, like the L21 and the D5x/E5x: USART Features Full-duplex Operation Asynchronous (with Clock Reconstruction) or Synchronous Operation Internal or External Clock source for Asynchronous and Synchronous Operation ... Supports Serial Frames with 5, 6, 7, 8 or 9 Data bits and 1 or 2 Stop bits Odd or Even Parity Generation and Parity Check Selectable LSB- or MSB-first Data Transfer ... Note that neither mark or space are supported for parity, but you can transfer 9 data bits. The data register is 16 bits wide to support using 9 data bits. If you want to drive people really mad, you use 9 bit mode with parity enabled and two stop bits. This ends with a line format of 13 bits (1 start + 9 data + 1 parity + 2 stop bits), and only a few other U(S)ARTs will be able to send or receive that format. Alexander -- Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)	[reply] [d/l]
Re^7: How to read serial port with WIN32:SerialPort? by jmlynesjr (Deacon) on Apr 16, 2021 at 01:46 UTC
Alexander: Thanks for comfirming my guess. I have not gotten around to reading the POD or code. I have nothing else to add to this topic. It was a good discussion. James There's never enough time to do it right, but always enough time to do it over...	[reply]

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