-- usart asynchronous serial routine
-- writen and tested in jal by Surducan Vasile
-- distributed under GPL licence ( all you see is yours, gave me some credits)
-- some ideea taken from picuart.asm by Thomas Mc.Gahee
include f877_20
-- uart initialization
-- -------------------------------------------------------------------------
pin_c6_direction = output -- tx
pin_c7_direction = input -- rx
bank_1
f877_txsta = 0b_0010_0100 ; asynch mode, 8bit, transmit enable, high speed
; f877_txsta = 0b_0010_0000 ; asynch mode, 8bit, transmit enable, low speed
f877_spbrg = 10 ; set baudrate at 115200 bps; set your owns according the
; table below
bank_0
f877_rcsta = 0b_1001_0000 ; serial port enable, 8bit mode,
; constant reception
assembler
movf f877_rcreg, w -- clear uart receiver and 2 fifo's
movf f877_rcreg, w
movf f877_rcreg, w
movlw 0
movwf f877_txreg -- send out one dummy caracter
end assembler
-- end of usart initialization
-- -------------------------------------------------------
-- asynchronous mode
-- ------------------------------------------------------
-- xtal(MHz) baud_rate spbrg/brgh spbrg/brgh
-- ------------------------------------------------------
-- 20 1200 255 0 -
-- 20 2400 129 0 -
-- 20 4800 64 0 -
-- 20 9600 - 129 1
-- 20 19200 - 64 1
-- 20 28800 - 42 1
-- 20 33600 - 36 1
-- 20 38400 - 32 1
-- 20 57600 - 20 1
-- 20 115200 - 10 1
-- 20* 230400 - 4 1
-- ------------------------------------------------------
-- 10 1200 129 0 -
-- 10 2400 64 0 -
-- 10 4800 31 0 -
-- 10 9600 - 64 1
-- 10 19200 - 31 1
-- 10 28800 - 21 1
-- 10 33600 - 18 1
-- 10 38400 - 15 1
-- 10 57600 - 10 1
-- 10* 115200 - 4 1
-- ------------------------------------------------------
-- 4 300 207 0 -
-- 4 1200 51 0 -
-- 4 2400 25 0 -
-- 4 4800 12 0
-- 4 9600 - 25 1
-- 4 19200 - 12 1
-- 4* 28800 - 7 1
-- 4* 33600 - 6 1
-- ------------------------------------------------------
-- spbrg = (xtal[hz]/(baudrate[bps]*64))-1 for brgh=low
-- spbrg = (xtal[hz]/(baudrate[bps]*16))-1 for brgh=high
-- asynchronous mode
-- ------------------------------------------------------
-- * not tested
procedure async_rx ( byte out rx_data ) is
assembler
local ser_in, uart_ready, no_int, overerror,
frameerror
ser_in:
btfsc f877_rcsta,oerr
goto overerror -- to overflow error...
btfsc f877_rcsta,ferr
goto frameerror -- to framing error...
uart_ready:
btfss f877_pir1,rcif
goto ser_in -- wait if not ready...
no_int:
bcf intcon_gie -- switch off interrupts
btfsc intcon_gie -- be sure
goto no_int
movf f877_rcreg,w -- recover uart data
bsf intcon_gie -- re-enable interrupts
movwf rx_data -- save in reception register
return
overerror: -- if f877_rcreg is still full at third byte stop bit detection
bcf intcon_gie -- turn interrupts off
btfsc intcon_gie -- be sure
goto overerror
bcf f877_rcsta,cren -- disable continuous receive, reset oerr
movf f877_rcreg,w -- flush rcreg + 2 fifo, this will clears the
movf f877_rcreg,w -- ferr flag
movf f877_rcreg,w
bsf f877_rcsta,cren -- enable continous receive, clear oerr
bsf intcon_gie -- enable interrupts.
goto ser_in -- try again...
frameerror: -- if garbage is coming in
bcf intcon_gie -- disable interrupts
btfsc intcon_gie
goto frameerror -- be sure
movf f877_rcreg,w -- reading rcreg clears ferr flag
-- bcf f877_rcsta,ferr -- sure clears ferr
bsf intcon_gie
goto ser_in
end assembler
end procedure
procedure async_tx ( byte in tx_data ) is
assembler
local transmit, interrupt
movf tx_data,w -- copy tx_data to w.
transmit:
btfss f877_pir1,txif
goto transmit -- wait for transmitter interrupt flag
interrupt:
bcf intcon_gie -- disable interrupts
btfsc intcon_gie -- be sure
goto interrupt
movwf f877_txreg -- load data to be sent...
bsf intcon_gie -- re-enable interrupts
return -- transmitted data is in W
end assembler
end procedure
var byte data
forever loop
async_rx ( data ) -- receive a character ( 8,N,1, hardware flow DTR=DSR,
-- RTS=CTS or none )
async_tx ( data ) -- send back to terminal
end loop
(
geocities.com/vsurducan/electro) (
geocities.com/vsurducan)