R. Koekoek |
|||||
The project described here can measure a frequency up to 100 kHz
with a deviation of only one alternation in 65,536. The frequency is displayed over five digits. The program
is written for the KIM but is usable on other 6502 microcomputers, like the SYM and the Junior.
The program will perform a frequency measurement only once after the "0" key is pressed, or it will measure
continuously after the "6" key is pressed.
|
To make this timing accurate and trim the measurement, an extra delay routine of about 3 ms is required. The accumulator, the
carry- and overflow-flag are cleared, then the number of overflows are counted until the next interrupt.
Counting is done in binary with the least significant bits in the X-register, then the Y-register and the most significant bits in the accumulator. By keeping this routine as short as possible, the maximum frequency is about 100 kHz. The error occuring at 65536 pulses is arises when the X and Y-registers reach FFFF hex and the accumulator needs to be incremented. This makes the counting routine a little longer. Whenever an interrupt occurs, the interrupt routine is being called. Here the timer is being restarted if this was not the fourth interrupt. If it was the fourth, the value is converted to decimal. This happens only now because counting in decimal happens in the accumulator and is more time consuming. Conversion from binary to decimal is done as follows: in the table there are respectively the decimal values of 1, 10, 100, 1,000 and 10,000. As long as the value is not negative, the 10,000 counter is incremented. The result is being put back in the original counter. If the result was negative, the value of the counter before the subtraction is used and the next value from the table is subtracted. This goes on until the counter reaches zero. The decimal value is kept in the readout registers. After the conversion, the display lights up and shows the value. Next the key is checked. If not, the preveous key value is used. If yes, the program stops measuring at a "0" and goes on displaying the frequency at a "6". | Radio Bulletin | January 1981 | ||
|
Adjustment The adjustment goes as follows. A dividing circuit, composed of two devide-by-10 deviders, is connected to the 1 MHz clock of the computer. The frequency at the output will be in the neighbourhood of 10 kHz. This signal is being fed to input and |
the program is started. By modifying the values in memory locations 021C and 021E of the delay-routine, the readout is adjusted to 10.000. The devide-by-100 is used because then the accumulator is not yet active in the proces. This way the meter is most accurate. By connecting the devider between the buffer(7413) and the RO (SO) input the measurement is extended to 10 MHz. In order to make the timer work it's importand for the KIM to connect PB7 (A-15) and NMI (E-6) and for the Junior, NMI (12-C) and IRQ (12-A). The timer actualy generates interupts. | Modifications for the Junior The program in the listing is for the KIM. For the Junior the following changes apply: Address KIM Junior 0203 FB 7B 0204 17 1A 0208 FA 7A 0209 17 1A 0219 0F FF 021A 17 1A 0283 1F 8E 0284 1F 1D 02A0 0F FF 02A1 17 1A |
MICRO-WARE ASSEMBLER 65XX-1.0 PAGE 01
0010:
0020: *****************************************
0030: * *
0040: * FREQUENCY COUNTER *
0050: * FOR THE 6502 *
0060: * *
0070: * AUTHORS : M. DOHMEN *
0080: * R. KOEKOEK *
0090: * *
0100: *****************************************
0110:
0120: 0200 ORG $0200
0130:
0140: ZEROPAGE ADDRESSES
0150:
0160: 0200 INTCNT * $00D0
0170: 0200 ZEROP * $00D1
0180: 0200 TEMPC * $00E0
0190: 0200 TEMPB * $00E1
0200: 0200 TEMPA * $00E2
0210: 0200 INL * $00F8
0220: 0200 INH * $00F9
0230: 0200 POINTL * $00FA
0240: 0200 POINTH * $00FB
0250: 0200 CHAR * $00FE
0260:
0270: TABLE
0280:
0290: 0200 TABLO * $02AF
0300: 0200 TABHI * $02B0
0310:
0320: TIMERADDRESS
0330:
0340: 0200 TIMER * $170F
0350:
0360: INTERRUPT VECTOR
0370:
0380: 0200 INTLO * $17FA
0390: 0200 INTHI * $17FB
0400:
0410: MONITOR SUBROUTINE
0420:
0430: 0200 SCANDS * $1F1F
0440:
0450: MAIN PROGRAM
0460:
0470: 0200 A9 02 INIT LDAIM $02
0480: 0202 8D FB 17 STA INTHI
0490: 0205 A9 98 LDAIM $98 SET INTERRUPT VECTOR
0500: 0207 8D FA 17 STA INTLO
0510: 020A A9 FC START LDAIM $FC SET INTERRUPT COUNTER
0520: 020C 85 D0 STA INTCNT TO -4
0530: 020E A9 00 LDAIM $00
0540: 0210 85 F9 STA INH CLEAR DISPLAY AND
0550: 0212 85 FA STA POINTL COUNTER
0560: 0214 85 FB STA POINTH
0570: 0216 A9 F5 LDAIM $F5 SET TIMER AND
0580: 0218 8D 0F 17 STA TIMER ENABLE INTERRUPTS
0590:
0600: EXTRA DELAY ROUTINE
0610:
0620: 021B A2 03 LDXIM $03 ADJUST THESE
0630: 021D A0 00 BULOOP LDYIM $00 VALUES FOR
0640: 021F 88 BILOOP DEY REQUIRED PRECISION
0650: 0220 D0 FD BNE BILOOP
0660: 0222 CA DEX
0670: 0223 D0 F8 BNE BULOOP
0680:
0690: COUNT PROGRAM
0700:
0710: 0225 B8 CLV
0720: 0226 18 CLC
0730: 0227 98 TYA CLEAR ACCU
0740: 0228 50 FE OVERFL BVC OVERFL OVERFLOW SET?
0750: 022A B8 CLV
0760: 022B E8 INX ADD 1 TO X
0770: 022C D0 FA BNE OVERFL X = FF ?
0780: 022E C8 INY ADD 1 TO Y
0790: 022F D0F7 BNE OVERFL Y = FF ?
0800: 0231 69 01 ADCIM $01 ADD 1 TO ACCU
0810: 0233 D0 F3 BNE OVERFL ACCU = FF? |
0820: 0830: BINARY TO DECIMAL CONVERSION 0840: 0850: 0235 85 E2 BINDEC STA TEMPA SAVE ACCU 0860: 0237 84 E1 STY TEMPB SAVE Y 0870: 0239 86 E0 STX TEMPC SAVE X 0880: 023B A2 08 LDXIM $08 SET POINTER 0890: 023D A5 E2 POS LDA TEMPA 0900: 023C C9 00 CMPIM $00 IS COUNTER 0910: 0241 D0 0C BNE SUBT STILL BIGGER 0920: 0243 A5 E1 LDA TEMPB THAN THE 0930: 0245 DD B0 02 CMPAX TABHI ACTUAL 0940: 0248 D0 05 BNE SUBT VALUE 0950: 024A A5 E0 LDA TEMPC IN THE 0960: 024C DD AF 02 CMPAX TABLO TABLE 0970: 024F 90 2D SUBT BCC NEXT NO? GET NEXT TABLE VALUE 0980: 0251 38 SEC YES? SUBSTRACT 0990: 0252 A5 E0 LDA TEMPC THE ACTUAL 1000: 0254 FD AF 02 SBCAX TABLO VALUE IN 1010: 0257 85 E0 STA TEMPC THE TABLE 1020: 0259 A5 E1 LDA TEMPB FROM 1030: 025B FD B0 02 SBCAX TABHI THE 1040: 025E 85 E1 STA TEMPB VALUE IN 1050: 0260 A5 E2 LDA TEMPA THE COUNTER 1060: 0262 E9 00 SBCIM $00 1070: 0264 85 E2 STA TEMPA AND PUT COUNTER BACK 1080: 0266 8A TXA SAVE TABLEPOINTER 1090: 0267 48 PHA IN X ONTO THE STACK 1100: 0268 4A LSRA FIND OUT IN WHICH DIGIT 1110: 0269 4A LSRA THE COUNTERVALUE SHOULD COME 1120: 026A AA TAX BY MEANS OF POINTER IN X 1130: 1140: COUNTER VALUE IN DECIMAL TO DISPLAY 1150: 1160: 026B B0 04 BCS TIENT IS IT A DECADE? 1170: 026D F6 F9 INCZX INH NO? ADD ONE 1180: 026F D0 09 BNE NOG AND RETURN 1190: 0271 B5 F9 TIENT LDAZX INH GET PREVEOUS VALUE 1200: 0273 69 0F ADCIM $0F AND ADD DECADE 1210: 0275 95 F9 STAZX INH DISPLAY 0040: 027A 68 NOG PLA GET TABLEPOINTER FROM STACK 0050: 027B AA TAX AND PUT THAT IN X 0060: 027C 10 BF BPL POS ALL READY? 0070: 027E CA NEXT DEX TABLE POINTER TO 0080: 027F CA DEX NEXT VALUE 0090: 0280 10 BB BPL POS AND BACK 0100: 0282 20 1F 1F DISPL JSR SCANDS DISPLAY COUNTER 0110: 0285 D0 0B BNE KEY KEY PRESSED? 0120: 0287 A5 F8 LDA INL NO? GET PREVEOUS 0130: 0289 D0 02 BNE DI WAS IT ZERO? 0140: 028B C6 D1 DEC ZEROP NO? DISPLAY 0150: 028D D0 F3 DI BNE DISPL JA? KEEP DISPLAYING 0160: 028F 4C 0A 02 BACK JMP START RESTART 0170: 0292 4A KEY LSRA 0180: 0293 85 F8 STA INL SAVE KEY 0190: 0295 4C 0A 02 JMP START RESTART 0200: 0210: INTERRUPT ROUTINE 0220: 0230: 0298 48 PHA SAVE ACCU 0240: 0299 E6 D0 INC INTCNT DECREMENT COUNTER 0250: 029B F0 07 BEQ VIER FOURTH INTERRUPT? 0260: 029D A9 F5 LDAIM $F5 NO, LOAD TIMER AND 0270: 029F 8D 0F 17 STA TIMER ENABLE INTERRUPT 0280: 02A2 68 PLA GET ACCU BACK 0290: 02A3 40 RTI AND RETURN 0300: 02A4 68 VIER PLA GET ACCU BACK 0310: 02A5 85 FE STA CHAR SAVE DATA 0320: 02A7 68 PLA 0330: 02A8 68 PLA ADJUST STACK 0340: 02A9 68 PLA 0350: 02AA A5 FE LDA CHAR GET DATA BACK 0360: 02AC 4C 35 02 JMP BINDEC CONVERT 0370: 02AF 01 = $01 0380: 02B0 00 = $00 0390: 02B1 0A = $0A 0400: 02B2 00 = $00 0410: 02B3 64 = $64 0420: 02B4 00 = $00 0430: 02B5 E8 = $E8 0440: 02B6 03 = $03 0450: 02B7 10 = $10 0460: 02B8 27 = $27 |
|||
| Radio Bulletin | January 1981 | |||