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ljbeng
Joined: 10 Feb 2004
Posts: 205
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| Change Baud and Parity on-the-fly |
 Posted: Tue Apr 26, 2005 7:56 am |
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I am rehashing this from another post..
I want to Receive at 300,o,8,1. I want to transmit at 9600,n,8,1.
The chip is 18F452 and I want to use the hardware UART.
If I comment out the set_uart_speed(); lines, the device will transmit at 300 baud no parity so resetting the parity bit for transmit works. It seems changing to 9600 baud and then turning off parity is not working.
| Code: |
//abbreviated code....
#use rs232(baud=300,parity=O,xmit=PIN_C6,rcv=PIN_C7,bits=8,errors)
#int_RDA
RDA_isr(){
//receive 300 odd parity here
}
main(){
//do stuff....
//if I need to transmit data....
if (txresp){
disable_interrupts(INT_RDA);
set_uart_speed(9600);
#asm
BCF 0xFAC.6 // clears the 9 bit transmit enable bit
#endasm
txresp = 0;
putc('@');
putc('h');
putc('i');
set_uart_speed(300);
enable_interrupts(INT_RDA);
}
}
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Here is the listing....
You can see 66 gets moved into FAC then I reset bit 6 of FAC to turn off parity transmission.
| Code: |
.................... if (txresp){
523C: MOVF x7B,F
523E: BZ 5296
.................... disable_interrupts(INT_RDA);
5240: BCF F9D.5
.................... putc(0);
5242: MOVLB 2
5244: CLRF x37
5246: MOVLB 0
5248: CALL 3FFA
.................... set_uart_speed(9600);
524C: MOVLW 1A
524E: MOVWF FAF
5250: MOVLW 66
5252: MOVWF FAC
.................... #asm
.................... BCF 0xFAC.6
5254: BCF FAC.6
.................... #endasm
.................... txresp = 0;
5256: MOVLB 1
5258: CLRF x7B
.................... putc('@');//0x80);
525A: MOVLW 40
525C: MOVLB 2
525E: MOVWF x37
5260: MOVLB 0
5262: CALL 3FFA
.................... putc('h');//remoteid);
5266: MOVLW 68
5268: MOVLB 2
526A: MOVWF x37
526C: MOVLB 0
526E: CALL 3FFA
.................... putc('i');//~remoteid);
5272: MOVLW 69
5274: MOVLB 2
5276: MOVWF x37
5278: MOVLB 0
527A: CALL 3FFA
.................... putc(' ');//func);
527E: MOVLW 20
5280: MOVLB 2
5282: MOVWF x37
5284: MOVLB 0
5286: CALL 3FFA
.................... set_uart_speed(300);
528A: MOVLW D4
528C: MOVWF FAF
528E: MOVLW 62
5290: MOVWF FAC
.................... enable_interrupts(INT_RDA);
5292: BSF F9D.5
5294: MOVLB 1
3FFA: MOVLW 08
3FFC: MOVWF 01
3FFE: MOVLB 2
4000: CLRF x38
4002: INCF x38,F
4004: MOVFF 237,00
4008: MOVF 00,W
400A: XORWF x38,F
400C: RRCF 00,F
400E: DECFSZ 01,F
4010: BRA 4008
4012: BTFSS F9E.4
4014: BRA 4012
4016: MOVLW FE
4018: ANDWF FAC,F
401A: BTFSC x38.0
401C: BSF FAC.0
401E: MOVFF 237,FAD
4022: MOVLB 0
4024: RETLW 00
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ljbeng
Joined: 10 Feb 2004
Posts: 205
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| Posted: Tue Apr 26, 2005 8:13 am |
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| I added 10ms delays between the putc lines and it worked. The program must not be waiting for the TSR to empty before sending the next character and I must have been overrunning the buffer??? |
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Ttelmah
Guest
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| Posted: Tue Apr 26, 2005 9:17 am |
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The program does wait for the buffer to empty before adding another character, but there will still be characters 'in transit', after the last putc. You need to wait long enough for the character in the output shift register to send, and then the one in the transmitter buffer to move into the shift register, between the last putc, and changing the baud rate. By delaying between each character, you are ensuring that the last character, has actually transferred to the shift register, and the way the UART is meant to work, is that it won't change speeds, until a character 'in transit' in this register, has completed (some chips are faulty in this regard...), hence it then works.
If you just add a test after the last putc, for the transmitter buffer empty flag being set, before you change the rate, it should work.
Best Wishes |
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