GCBASIC documentation
RS232 (hardware)

Syntax:

Used as subroutine:

    HSerReceive (user_byte_variable)

or, if other multiple comports are in use, set the comport before using HSerReceive.

    comport = 1   '(1|2|3|4|5)Not needed unless using multiple comports in use
    HSerReceive (_user_byte_variable_)

or, used as function.

  user_byte_variable = HSerReceive  'Supports only USART1
  user_byte_variable = HSerReceive1 'Supports only USART1
  user_byte_variable = HSerReceive2 'Supports only USART2

or, used to support assigning of received byte to word (or other multi-byte variables).  Note the use of casting to ensure the HSerReceive uses byte addressing.

  Dim dbAdr as Word

  HSerReceive [byte]dbAdr_H
  HSerReceive [byte]dbAdr

For other comports use Function HSerReceiveFrom

Command Availability:

Available on all microcontrollers with a USART or UART module.

Microchip PIC supports USART1,2,3,4 and 5.
Atmel AVR supports USART 1,2,3 and 4.

Enabling Constants:

To enable the use of the USART these are the enabling constants.   These constants are required.  You can change the USART_BAUD_RATE and to meet your needs.  For addition USART ports use #define USARTn_BAUD_RATE 9600 where n` is the required port number.

    'USART settings for USART1
    #define USART_BAUD_RATE 9600       'Set the baud rate
    #define USART_TX_BLOCKING          'Ensure the transmit buffer is empty
    #define USART_BLOCKING             'Ensures a data byte is in the receive buffer
    #define USART_DELAY OFF	       'Disables USART delays

Explanation:

This command will read a byte from the hardware RS232 module. It can be used either as a subroutine or as a function. If used as a subroutine, a variable must be supplied to store the received value in. If used as a function, it will return the received value.

The subroutine HSerReceive can get a byte from any comport but must set the comport number immediately before the call. If #define USART_BLOCKING is defined, then HSerReceive waits in a loop until it receives a byte. If #define USART_BLOCKING is not defined, then HSerReceive returns the new byte that was received, or returns 255 because DefaultUsartReturnValue = 255 was defined. This is useful because it does not hold up your program from executing other commands, and you can check it for new data periodically.

Example:

  'This program will read a value from the USART, and send it to PORTB.

  #chip 16F877A, 20

  'USART settings
  #define USART_BAUD_RATE 9600  'sets up comport 1 for 9600 baud

  'Set PORTB to output
  Dir PORTB Out
  'Set USART receive pin to input
  Dir PORTC.7 In

  'Main loop
  Do
    'Get serial data and output value to PortB as 8 bit binary
    HSerReceive(InChar)  'Receive data as Subroutine from comport 1          ' <<< the HSerReceive instruction
    'InChar = HSerReceive  'Could also be written as Function
    If InChar <> 255 Then   'If value is 255 then it is old data
      PortB = InChar    'If new data then it goes to PortB
    End If
  Loop

Key line: HSerReceive(InChar) — reads a byte from comport 1 into InChar; without USART_BLOCKING defined, a value of 255 means no new byte has arrived yet.

Example 2:

  'If you choose no "Blocking" and comment both of them out.
  'USART settings
  #define USART_BAUD_RATE 9600
  '#define USART_BLOCKING        ' just none OR one of the blocking
  '#define USART_TX_BLOCKING    ' statements should be defined

  'Main loop
  Do
    'Get and display value
    'If there is no new data, HSerReceive will return default value.
    comport = 1
    HSerReceive tempvalue          ' <<< HSerReceive used as a subroutine with an explicit comport
    If tempvalue <> 255    Then    ' do not change PortB if it is the default value
      PortB = tempvalue
    End If

  Loop

Key line: HSerReceive tempvalue — setting comport immediately before the call directs this read to a specific USART port.

Example 3:

  'If you choose no "Blocking" and comment both of them out.
  #chip mega328p, 16

  #define USART_BAUD_RATE 9600
  '#define USART_BLOCKING
  '#define USART_TX_BLOCKING

  'Do not forget to set USART pin directions
  Dir PortD.1 Out    'com1   USART0
  Dir PortD.0 In

  Wait 1 s

  'Message after reset
  HSerPrint "ATmega328P  com test"
  HSerPrintCRLF

  'Main routine  hook up FTDI232 usb to serial and use terminal program to check
  Start:
    comport = 1
    HSerReceive(InChar)    'Subroutine needs the comport set
    'InChar = HSerReceive    ' This function will get from comport 1
      If InChar <> 255 Then    ' check if for received byte
                  'return 255 if old data
        HSerSend InChar    'send back char to UART
      End If
  Goto Start

See Also: