Mike McLaren - K8LH (Westland, MI) says:
Here is a Serial I/O demo for the 16F819 which uses 3X bit rate interrupts as well as Rx and Tx state machines in the ISR to achieve full-duplex 9600 baud serial I/O with 16-byte circular Tx and Rx buffers...
While this demo could easily be considered a novelty for using nearly 50%
of the overall processing time at 9600 baud with an 8-MHz clock, I suspect
it could be quite useful with a faster clock and/or at slower baud
rates...
list p=16F819, b=8, c= 102, n=71, t=on, st=off, f=inhx32 ;****************************************************************** ;* * ;* Filename: 16F819 Serial 1.asm * ;* Author: Mike McLaren, K8LH (k8lh_at_arrl.net) * ;* Date: 08-Jun-05 (last revision 12-Jun-05) * ;* * ;* Full Duplex Bit-Banged 9600 Baud Serial I/O Demo * ;* (based on a nearly identical 12F683 Demo) * ;* * ;* ·Uses 16F819 INTOSC running at 8-MHz * ;* ·Bit rate error 0.6% plus or minus 1.0% for INTOSC * ;* ·Bit-banged 9600 baud serial I/O * ;* ·Full Duplex (TX and RX simultaneously) * ;* ·Interrupts at approximately 3X bit rate every * ;* 34.5 usecs (every 69 instruction cycles) * ;* ·Circular 16-byte receive ahead buffer * ;* ·Circular 16-byte transmit ahead buffer * ;* ·Inverted TX and RX signals (MAX232A or similar * ;* inverting RS-232 interface required) * ;* ·ISR and Init232, Put232, and Get232 support routines * ;* fit comfortably in the first 192 words of code space * ;* occupying memory from 0004 through 00BF (188 words) * ;* * ;* MPLab: 7.11 (tabs=8) * ;* MPAsm: 4.01 * ;* * ;****************************************************************** #include <p16f819.inc> errorlevel -302 __config _LVP_OFF & _PWRTE_ON & _WDT_OFF & _INTRC_IO ; ; Serial I/O file register variables & buffers ; TX_RPTR equ 0x20 ; TX buffer Rd pointer (isr) TX_WPTR equ 0x21 ; TX buffer Wr pointer (main) TXCHAR equ 0x22 ; TX character (main, Put232) TXWORK equ 0x23 ; TX ISR work byte (isr) ; RX_RPTR equ 0x24 ; RX buffer Rd pointer (main) RX_WPTR equ 0x25 ; RX buffer Wr pointer (isr) RXCHAR equ 0x26 ; RX character (main, Get232) RXWORK equ 0x27 ; RX ISR work byte (isr) ; TX_SM equ 0x28 ; TX state machine var (isr) RX_SM equ 0x29 ; RX state machine var (isr) ; RXBUFF equ 0xA0 ; RX buffer, 16 bytes A0h-AFh TXBUFF equ 0xB0 ; TX buffer, 16 bytes B0h-BFh ; ; 16F819 serial port pin defines ; #define RXPIN PORTB,2 ; RS-232 RX (RB2) #define TXPIN PORTB,5 ; RS-232 TX (RB5) ; ; file locations used by ISR to save and restore context ; W_ISR equ 0x70 ; ISR 'W' S_ISR equ 0x71 ; ISR 'STATUS' P_ISR equ 0x72 ; ISR 'PCLATH' F_ISR equ 0x73 ; ISR 'FSR' ; ; other vars ; FSRTMP equ 0x74 ; Put232 & Get232 (main) PTRL equ 0x75 ; PutStr routine (main) PTRH equ 0x76 ; PutStr routine (main) ;****************************************************************** ; ; _Title macro - home cursor, clear screen, print a string ; _Title macro str ; local String, Print movlw low String ; movwf PTRL ; movlw high String ; movwf PTRH ; goto Print ; String dt h'1B',"[2J" ; <esc>[2J sequence dt str,0 Print call PutString ; print string endm ;****************************************************************** ; ; Hardware notes ; ; <1> INTOSC 8-MHz, 500-nsec instruction cycle time ; <2> RB2 (pin 08) > RXPIN, 'bit banged' serial input ; <3> RB5 (pin 11) > TXPIN, 'bit banged' serial output ; <4> RS-232 signals inverted (use MAX232A or similar) ; <5> ; <6> ; <7> ; ; ; This program simply prints a text string to Hyperterminal ; and echos characters coming from Hyperterminal... ; ; Setup Hyperterminal for 9600, 8, 1, none... Use a MAX232 or ; similar level shifting circuit (I use a pair of 2N7000s) for ; connection between the 16F819 and the PC... ; ;****************************************************************** ;* * ;* * ;* * ;* * ;* * ;****************************************************************** org 0x0000 RESET clrf STATUS ; |B0 goto MAIN ; |B0 ;****************************************************************** ;* * ;* Interrupt Service Routine for a Full Duplex Bit-Banged * ;* 9600 Baud Serial I/O with 16 byte circular receive and * ;* transmit buffers... * ;* * ;* Interrupts are generated at approximately 3 times the * ;* bit rate for 9600 baud at 34.5-usec intervals or every * ;* 69 instruction cycles. * ;* * ;* The transmit and receive processes are executed in the * ;* correct sequence each interrupt cycle by using a state * ;* machine variable and jump table for both RX and TX. * ;* * ;* After detecting a start bit, the receive bit stream is * ;* sampled every third interrupt cycle in the approximate * ;* middle third of each bit (between 33% and 66%). * ;* * ;* The 16 byte circular TXBUFF is located at B0..BF in RAM * ;* and will buffer 15 bytes. The "unload buffer" process * ;* is performed in the ISR after sending a character and * ;* the "load buffer" process is performed outside the ISR * ;* in the Put232 subroutine. * ;* * ;* The 16 byte circular RXBUFF is located at A0..AF in RAM * ;* and will buffer 15 bytes. The "load buffer" process is * ;* performed in the ISR after receiving a character and * ;* the "unload buffer" process is performed outside of the * ;* ISR in the Get232 subroutine. * ;* * ;* Of the 69 instruction cycles between interrupts the ISR * ;* uses between 34 and 35 cycles average each interrupt or * ;* approximately 49.3% to 50.7% of the overall processing * ;* time available. The TX code uses almost the same number * ;* of instruction cycles when transmitting or idle. The RX * ;* code uses 1 more instruction cycle average per interrupt * ;* when receiving than it does when idle. * ;* * ;* 34.0 cycles avg (49.3% mcu overhead) RX idle * ;* 35.0 cycles avg (50.7% mcu overhead) RX in progress * ;* * ;****************************************************************** org 0x0004 ; ; save main program context ; ; 09 cycles every interrupt cycle ; ISR movwf W_ISR ; save W-reg |B? swapf STATUS,W ; doesn't change STATUS bits |B? movwf S_ISR ; save STATUS reg |B? clrf STATUS ; bank 0 |B0 movf PCLATH,W ; get PCLATH |B0 movwf P_ISR ; save PCLATH |B0 bcf PIR1,TMR2IF ; clear TMR2 interrupt flag |B0 ; ; enter the TX state machine ; ; 06 cycles, including TX SM jump, every interrupt cycle ; clrf PCLATH ; |B0 movf TX_SM,W ; get TX state machine |B0 addwf PCL,f ; off we go |B0 ; ; the TX state machine table (cycle times include ISR entry, ; TX state machine jump, and RX state machine jump) ; ; TX idle, 24.0 of 69.0 instructions per interrupt (34.8%) ; TX proc, 24.0 of 69.0 instructions per interrupt (34.8%) ; goto TX_CHK ; TX idle 24 cycles |B0 goto TX_0 ; start bit 24 cycles |B0 goto TX_BUF ; 31 cycles |B0 goto TX_NXT ; 21 cycles |B0 goto TX_BIT ; bit 0 28 cycles |B0 goto TX_NXT ; 21 cycles |B0 goto TX_NXT ; 21 cycles |B0 goto TX_BIT ; bit 1 28 cycles |B0 goto TX_NXT ; 21 cycles |B0 goto TX_NXT ; 21 cycles |B0 goto TX_BIT ; bit 2 28 cycles |B0 goto TX_NXT ; 21 cycles |B0 goto TX_NXT ; 21 cycles |B0 goto TX_BIT ; bit 3 28 cycles |B0 goto TX_NXT ; 21 cycles |B0 goto TX_NXT ; 21 cycles |B0 goto TX_BIT ; bit 4 28 cycles |B0 goto TX_NXT ; 21 cycles |B0 goto TX_NXT ; 21 cycles |B0 goto TX_BIT ; bit 5 28 cycles |B0 goto TX_NXT ; 21 cycles |B0 goto TX_NXT ; 21 cycles |B0 goto TX_BIT ; bit 6 28 cycles |B0 goto TX_NXT ; 21 cycles |B0 goto TX_NXT ; 21 cycles |B0 goto TX_BIT ; bit 7 28 cycles |B0 goto TX_NXT ; 21 cycles |B0 goto TX_NXT ; 21 cycles |B0 goto TX_PTR ; stop bit 28 cycles |B0 goto TX_NXT ; 21 cycles |B0 goto TX_RES ; reset 23 cycles |B0 ; ; perform TX "unload buffer" function and send the stop bit ; ; 13 cycles, including RX SM jump, 01 in 30 TX cycles ; TX_PTR incf TX_RPTR,W ; W = TX_RPTR + 1 |B0 andlw h'0F' ; keep in range 00..0F |B0 addlw TXBUFF ; make it range B0..BF |B0 movwf TX_RPTR ; update TX_RPTR |B0 bsf TXPIN ; send stop bit |B0 goto TX_NXT ; increment TX state |B0 ; ; reset TX state machine during final third of the stop bit ; for 138.5 usecs (1 and 1/3 bit times) between TX characters ; TX_RES clrf TX_SM ; reset TX state machine |B0 goto TX_XIT ; |B0 ; ; copy character from RXBUFF to TXWORK after sending start bit ; ; 17 cycles, including RX SM jump, 01 in 30 TX cycles ; TX_BUF movf FSR,W ; get FSR |B0 movwf F_ISR ; save it |B0 movf TX_RPTR,W ; get TX buffer Rd ptr [B0..BF] |B0 movwf FSR ; setup indirect address |B0 movf INDF,W ; get data |B0 movwf TXWORK ; put it in a work register |B0 movf F_ISR,W ; |B0 movwf FSR ; restore FSR |B0 goto TX_NXT ; increment TX state |B0 ; ; transmit bit ; ; 13 cycles, including RX SM jump, 08 in 30 TX cycles ; TX_BIT rrf TXWORK,f ; |B0 btfsc STATUS,C ; is it a '1'? |B0 TX_1 bsf TXPIN ; yes, send it |B0 btfss STATUS,C ; is it a '0'? |B0 TX_0 bcf TXPIN ; yes, send it |B0 goto TX_NXT ; increment TX state |B0 ; ; if there's a transmit character buffered, bump the TX_SM var ; to initiate the transmit process, else exit leaving TX_SM=00 ; ; 09 cycles, including RX SM jump, every interrupt cycle until ; a TX operation is initiated ; TX_CHK movf TX_RPTR,W ; get TX buffer Rd ptr [B0..BF] |B0 xorwf TX_WPTR,W ; xor TX buffer Wr ptr [B0..BF] |B0 btfss STATUS,Z ; skip empty (TX_RPTR=TX_WPTR) |B0 TX_NXT incf TX_SM,f ; inc TX state machine |B0 ;****************************************************************** ; ; enter the RX state machine (cycle times include ISR_XIT) ; ; RX idle, 10.0 of 69.0 instructions per interrupt (14.5%) ; RX proc, 11.0 of 69.0 instructions per interrupt (15.9%) ; TX_XIT movf RX_SM,W ; get RX state machine |B0 addwf PCL,f ; off we go |B0 ; ; the RX state machine table ; goto RX_CHK ; RX idle 10 cycles |B0 goto RX_NXT ; start bit 09 cycles |B0 goto RX_NXT ; 09 cycles |B0 goto RX_NXT ; 09 cycles |B0 goto RX_BIT ; bit 0 14 cycles |B0 goto RX_NXT ; 09 cycles |B0 goto RX_NXT ; 09 cycles |B0 goto RX_BIT ; bit 1 14 cycles |B0 goto RX_NXT ; 09 cycles |B0 goto RX_NXT ; 09 cycles |B0 goto RX_BIT ; bit 2 14 cycles |B0 goto RX_NXT ; 09 cycles |B0 goto RX_NXT ; 09 cycles |B0 goto RX_BIT ; bit 3 14 cycles |B0 goto RX_NXT ; 09 cycles |B0 goto RX_NXT ; 09 cycles |B0 goto RX_BIT ; bit 4 14 cycles |B0 goto RX_NXT ; 09 cycles |B0 goto RX_NXT ; 09 cycles |B0 goto RX_BIT ; bit 5 14 cycles |B0 goto RX_NXT ; 09 cycles |B0 goto RX_NXT ; 09 cycles |B0 goto RX_BIT ; bit 6 14 cycles |B0 goto RX_NXT ; 09 cycles |B0 goto RX_NXT ; 09 cycles |B0 goto RX_BIT ; bit 7 14 cycles |B0 goto RX_BUF ; buffer 19 cycles |B0 goto RX_NXT ; 09 cycles |B0 goto RX_NXT ; stop bit 09 cycles |B0 goto RX_PTR ; ptr & reset 18 cycles |B0 ; ; copy completed character in RXWORK byte to RXBUFF ; ; 19 cycles, including ISR_XIT, 01 in 30 RX cycles ; RX_BUF movf FSR,W ; |B0 movwf F_ISR ; save FSR |B0 movf RX_WPTR,W ; RX buffer Wr pointer [A0..AF] |B0 movwf FSR ; setup indirect address |B0 movf RXWORK,W ; get completed work byte |B0 movwf INDF ; place it in the RX buffer |B0 movf F_ISR,W ; |B0 movwf FSR ; restore FSR |B0 goto RX_NXT ; increment RX state |B0 ; ; receive bit ; ; 14 cycles, including ISR_XIT, 08 in 30 RX cycles ; RX_BIT btfsc RXPIN ; is it a 0? |B0 bsf STATUS,C ; no, make it a 1 |B0 rrf RXWORK,f ; shift into our work byte |B0 goto RX_NXT ; increment RX state |B0 ; ; perform RX buffer 'load' function after receiving byte ; ; 18 cycles, including ISR_XIT, 01 in 30 RX cycles ; RX_PTR incf RX_WPTR,W ; |B0 andlw RXBUFF+h'0F' ; |B0 xorwf RX_RPTR,W ; buffer full (WPTR+1=RPTR)? |B0 bz RX_RES ; yes, branch |B0 xorwf RX_RPTR,W ; no, restore WPTR+1 value |B0 movwf RX_WPTR ; update WPTR |B0 ; ; reset RX state machine after receiving a complete character ; and during the last 3rd (66%-100%) of the stop bit to allow ; setup time for detecting the next start bit ; RX_RES clrf RX_SM ; reset RX state machine |B0 goto ISR_XIT ; |B0 ; ; test for start bit (low) ; ; 10 cycles, including ISR_XIT, each cycle until RX initiated ; RX_CHK btfss RXPIN ; start bit? |B0 RX_NXT incf RX_SM,f ; inc RX state machine |B0 ; ; 08 cycles each interrupt cycle ; ISR_XIT movf P_ISR,W ; |B0 movwf PCLATH ; restore PCLATH |B0 swapf S_ISR,W ; |B0 movwf STATUS ; restore STATUS |B? swapf W_ISR,f ; don't screw up STATUS |B? swapf W_ISR,W ; restore W-reg |B? retfie ; return from interrupt |B? ;****************************************************************** ;* * ;* Companion Put232 and Get232 subroutines * ;* * ;****************************************************************** ; ; Put232 - enter with character to be sent in W ; - performs TXBUFF 'load buffer' operation ; Put232 movwf TXCHAR ; save character |B0 Pwait incf TX_WPTR,W ; W = WPTR + 1 |B0 andlw h'0F' ; keep it in range 00..0F |B0 addlw TXBUFF ; make it in range B0..BF |B0 movwf RXCHAR ; save here temporarily |B0 xorwf TX_RPTR,W ; buffer full (WPTR+1=RPTR)? |B0 bz Pwait ; yes, branch, wait |B0 movf FSR,W ; get FSR |B0 movwf FSRTMP ; save it |B0 movf TX_WPTR,W ; get TX buffer Wr ptr (B0..BF) |B0 movwf FSR ; setup indirect address |B0 movf TXCHAR,W ; get character |B0 movwf INDF ; place it in TX buffer |B0 movf FSRTMP,W ; |B0 movwf FSR ; restore FSR |B0 movf RXCHAR,W ; get saved TX_WPTR+1 value |B0 movwf TX_WPTR ; update TX_WPTR |B0 movf TXCHAR,W ; restore W entry data |B0 return ; |B0 ; ; Get232 - exit with received character in W & RXCHAR var ; - performs RXBUFF 'unload buffer' operation ; Get232 movf RX_RPTR,W ; |B0 xorwf RX_WPTR,W ; RPTR = WPTR (buff empty)? |B0 bz Get232 ; yes, loop, wait for character |B0 movf FSR,W ; |B0 movwf FSRTMP ; save FSR |B0 movf RX_RPTR,W ; |B0 movwf FSR ; setup indirect address |B0 movf INDF,W ; get RXBUFF[RPTR] character |B0 movwf RXCHAR ; save it for later |B0 movf FSRTMP,W ; |B0 movwf FSR ; restore FSR |B0 incf RX_RPTR,W ; W = RX_RPTR+1 |B0 andlw RXBUFF+h'0F' ; keep it in range of A0..AF |B0 movwf RX_RPTR ; update RX_RPTR |B0 movf RXCHAR,W ; get receive character |B0 return ; |B0 ;****************************************************************** ;* * ;* Companion Init232 subroutine * ;* * ;****************************************************************** ; ; initialize RS-232 variables before turning on interrupts ; Init232 clrf RX_SM ; clr RX state machine var |B0 clrf TX_SM ; clr TX state machine var |B0 movlw RXBUFF ; RX circular buffer address |B0 movwf RX_RPTR ; set RX buffer Rd pointer |B0 movwf RX_WPTR ; set RX buffer Wr pointer |B0 movlw TXBUFF ; TX circular buffer address |B0 movwf TX_RPTR ; set TX buffer Rd pointer |B0 movwf TX_WPTR ; set TX buffer Wr pointer |B0 ; ; put TXPIN latch in the stop condition and setup TRIS data ; direction for TXPIN output and RXPIN input (select bank 1 ; to access the TRIS register instead of the PORT register) ; bsf TXPIN ; put TXPIN latch in stop state |B0 bsf STATUS,RP0 ; select Bank 1 for TRIS access |B1 bcf TXPIN ; set TXPIN as output |B1 bsf RXPIN ; set RXPIN as input |B1 ; ; configure TIMER2 for 34.5-usec interrupts (8-MHz clock) ; ; note: INTCON is 00000000 after any reset ; T2CON is 00000000 after any reset (pre=1, post=1) ; PIE1 is 000-0000 after any reset ; PIR1 is 000-0000 after any reset ; bsf PIE1,TMR2IE ; enable TMR2 interrupts |B1 movlw d'69'-1 ; number of 500-nsec ticks |B1 movwf PR2 ; 34.5-usec interrupts |B1 bcf STATUS,RP0 ; select Bank 0 |B0 bsf INTCON,GIE ; enable global interrupts |B0 bsf INTCON,PEIE ; enable peripheral interrupts |B0 bsf T2CON,TMR2ON ; start TMR2 |B0 return ; |B0 ;****************************************************************** ; ; Print String - enter with string address in PTRL & PTRH ; PutString call GetTable ; get a table character |B0 andlw b'11111111' ; |B0 btfsc STATUS,Z ; last character? |B0 return ; yes, return |B0 call Put232 ; output char |B0 incfsz PTRL,F ; increment pointer |B0 goto PutString ; |B0 incf PTRH,F ; |B0 goto PutString ; |B0 ; GetTable movf PTRH,W ; |B0 movwf PCLATH ; |B0 movf PTRL,W ; |B0 movwf PCL ; |B0 ;****************************************************************** ;* * ;* * ;* * ;* * ;* * ;****************************************************************** MAIN clrf CCP1CON ; capture/compare module off |B0 bsf STATUS,RP0 ; bank 1 |B1 movlw h'06' ; |B1 movwf ADCON1 ; turn ADC module off |B1 movlw b'11111111' ; |B1 movwf TRISA ; set Port A all inputs |B1 clrf TRISB ; set Port B all outputs |B1 ; ; setup INTOSC for 8-MHz and wait for oscillator to stabilize ; movlw b'01110000' ; |B1 movwf OSCCON ; 8-mhz INTOSC system clock |B1 STABLE btfss OSCCON,IOFS ; oscillator stable? |B1 goto STABLE ; no, branch |B1 bcf STATUS,RP0 ; bank 0 |B0 ; ; Initialize RS-232 Serial I/O ; call Init232 ; Initialize RS-232 Serial I/O |B0 ; ; _Title macro - home cursor, clear screen, and print a string ; _Title "K8LH 16F819 Full Duplex Serial I/O Demo\r\n\n" ; ; Echo characters coming from Hyperterminal... ; TEST call Get232 ; receive character |B0 call Put232 ; echo character |B0 goto TEST ; loop forever |B0 ; ;****************************************************************** end
file: /Techref/microchip/16F819-rs232-9600-mm.htm, 27KB, , updated: 2005/6/13 19:39, local time: 2024/8/14 22:22,
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