; Description: ; Determine Baud Rate Of Serial Port By Timing Start Bit. ; ; Entry Requirements: ; None ; ; On Exit: ; B/A Has Current Baud Rate (As 9600, 1900, etc For Displaying) ; R0 Has Value For SMOD Bit Used ; R1 Has Divisor Rate Used ; ; Affected: ; SCON, SBUF, TMOD, TH0, TL0, R0, R1, B, A, DPTR, PSW ; ; Stack: ; 0 Bytes, Not Including Space Used By Called Routines ; ; Comments: ; The Tables Are Setup To Allow +-3% Variation In Timing. If Can't ; Get A Good Baud Rate, Just Keep Trying. The Routine Can And Will ; Be Tricked If Not Running At 8/N/1. ; AUTOBAUD: clr es ; No Serial Interrupts clr et0 ; No Timer 0 Interrupt mov scon,#052h ; Mode 3 Serial Port mov tmod,#021h ; Timer 1 Mode 2, Timer 0 Mode 1 mov sbuf,#000h ; Send A Null For First Character setb tr1 ; Start Timer 1 Up ; ; Wait For Start Bit, Run Timer While Start Bit High ; loop0: clr ri ; Ignore Any Character In SBUF clr tr0 ; Cancel Timer 0 mov th0,#000h ; Clear Timer 0 High mov tl0,#000h ; Clear Timer 0 Low jb p3.0,$ ; Wait For Start Bit High setb tr0 ; Start Timer 0 Running jnb p3.0,$ ; Wait For Start Bit To Go Low clr tr0 ; Cancel Timer 0 ; ; Timer 0 Has Start Bit Period. Test Against Table. ; mov dptr,#Table ; Point To Table loop1: mov a,#0 ; Set For MOVC movc a,@a+dptr ; Get High Byte From Table cjne a,th0,loop2 ; Compare mov a,#1 ; Set For MOVC movc a,@a+dptr ; Get Low Byte From Table cjne a,tl0,loop2 ; Compare loop2: jc loop4 ; If Greater, Try Next Entry mov a,#2 ; Set For MOVC movc a,@a+dptr ; Get High Byte From Table cjne a,th0,loop3 ; Compare mov a,#3 ; Set For MOVC movc a,@a+dptr ; Get Low Byte From Table cjne a,tl0,loop3 ; Compare setb c ; Flip Status loop3: jnc loop4 ; If Less, Try Next Entry ; mov a,#4 ; Point To SMOD Status Byte movc a,@a+dptr ; Get SMOD Byte mov r0,a ; Move To R0 For Return mov pcon,a ; Store It Back mov a,#5 ; Point To Speed Byte movc a,@a+dptr ; Get Speed Byte mov r1,a ; Move To R1 For Return mov th1,a ; Setup Baud Rate Timer mov tl1,a ; Setup Baud Rate Timer jnb ri,$ ; Wait For Character clr ri ; Say Character Received Isn't There mov a,#6 ; Offset To Baud Rate High movc a,@a+dptr ; Get High Of Baud Rate In Binary mov b,a ; Store In B mov a,#7 ; Offset To Baud Rate Low movc a,@a+dptr ; Get Low Of Baud Rate In Binary setb es ; Allow Serial Interrupts ret ; Return To Caller ; loop4: mov a,#8 ; Number Bytes In Record add a,dpl ; Add In DPL mov dpl,a ; Back To DPL jnc loop5 ; If No Carry, Skip inc dph ; Increment High Of DPTR loop5: clr a ; Clear For MOVC movc a,@a+dptr ; Get Byte cjne a,#-1,loop1 ; While Not -1, Loop sjmp loop0 ; Try Again ; ; All Values Calculated For 11.059200Mhz ; Table: dw 6328, 5960, 00040h, 00150 ; 150 dw 3164, 2980, 000a0h, 00300 ; 300 dw 2109, 1987, 000c0h, 00450 ; 450 dw 1582, 1490, 000d0h, 00600 ; 600 dw 0791, 0745, 000e8h, 01200 ; 1200 dw 0527, 0497, 000f0h, 01800 ; 1800 dw 0396, 0372, 000f4h, 02400 ; 2400 dw 0264, 0248, 000f8h, 03600 ; 3600 dw 0198, 0186, 000fah, 04800 ; 4800 dw 0132, 0124, 000fch, 07200 ; 7200 dw 0099, 0093, 000fdh, 09600 ; 9600 dw 0066, 0062, 000feh, 14400 ; 14400 dw 0049, 0047, 080fdh, 19200 ; 19200 dw -1 end
Source: Assorted Utilities, John C. Wren 11/23/96
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