In SX Microcontrollers, SX/B Compiler and SX-Key Tool, g_daubach wrote:

Bob,

Problem #1:

_bank is a marco that is declared somewhere at the beginning of the source code like this:

; For SX18/20/28 change FSR bits 7...5,
;  for SX48/52 change FSR bits 6...4
;
_bank macro 1
  bank \1			
  IFDEF SX48_52		; For SX48/52 change
    IF \1 & %10000000 	;  FSR bit 7
      setb fsr.7
    ELSE
      clrb fsr.7
    ENDIF
  ENDIF
endm

It makes sure that FSR bit 7 is correctly set for SX48/52 devices as the bank instruction does not modify bit 7. When you use the SX 28, you don't need the macro, and simply change "_bank" into "bank".

Problem #2:

UARTfs = 230400 is the sample frequency, it defines how often the UART input pins are sampled per second. With a clock frequency of 50 MHz, and an interrupt period of 217, UARTfs is 50 MHz / 217 = 230.4 kHz or 230400 Hz.

Num = 4 - Yes, you are right, this means that the UART code is called every fourth interrupt call.

Int Period = 217 - Yes, this means that the interrupt is fired every 217th clock cycle.

UARTDivide1 = UARTfs/(UARTbaud1*Num) - Yes, this calculates the number of executions of the UART transmit code for one bit length.

UARTStDelay1=UARTDivide1 + (UARTDivide1/2)+1 - After the receiver has detected a start bit, it requires a 1.5 bit time delay to "hit" the first received data bit "in the middle". After the first bit has been read, a delay time of just UARTDivide1 is required to "hit" the next bits "in the middle".

To set the Baud rates to 2400, use the following definitions:

UARTDivide1 = UARTfs/(2400*Num)
UARTDivide2 = UARTfs/(2400*Num)

This would set the UARTS to 2400-8-N-1

BTW: This UART code example is pretty complex - you can find another example in my SX book, and you may download the book code samples from here:
[url]http://www.parallax.com/Portals/0/Downloads/src/prod/sx/ProgSXEdPre.zip[/url]

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