As you can see, hookup it pretty trivial. So would be the code if BASIC-52 would have PORT3 access operator as for PORT1. As I wanted to keep the PORT1 pins for DS1302 clock hookup, I decided to use T0 and T1 pins for I2C interface. Dallas calls it 2-wire serial bus, but it is the same thing. They probably just can't use I2C name or Philips will sue their heads off.
Anyway, the first thing I needed was a way to read and write port 3 pins. BASIC-52 has a DBY() operator, but this accesses data RAM, not SFR address space where the P3 register is. So I created two very simple functions in shared RAM area (this means that you must have shared ram at 6000H, like this core conf). Before you actually run the program, you will need to tell BASIC-52 that you need the RAM for yourself by entering MTOP=05FFFH.
The code itself is very simple
6000: 85 b0 20 read: mov 020h,0b0h 22 ret 6004: 85 20 b0 write: mov 0b0h,020h 22 ret
This code is stored into shared RAM at lines 10000..10030. CALL operator is then used to read or write the port 3 value, with memory location 020h used as data exchange storage. The example source code below just runs in loop and outputs the current temperature reading. It does work but is very very slow. This kind of a functionality desperately calls for machine code implementation, but the BASIC code serves better as an example.
MTOP=05FFFH 10 REM DS1621 control 20 GOSUB 10000 25 GOSUB 2000 28 GOSUB 3000 : BY=090H : GOSUB 6000 : BY=0EEH : GOSUB 6000 : GOSUB 4000 : GOSUB 2000 30 GOSUB 3000 35 BY=090H : GOSUB 6000 36 BY=0AAH : GOSUB 6000 44 GOSUB 4000 46 GOSUB 3000 50 BY=091H : GOSUB 6000 60 GOSUB 7000 : GOSUB 8000 65 BH=BY 66 GOSUB 7000 : GOSUB 9000 70 GOSUB 4000 90 T=BH*256+BY 100 T=T/256 110 PRINT T 999 GOTO 30 1000 REM read P3 1010 CALL 6000H 1020 P3=DBY(020H) 1030 RETURN 1100 REM write P3 1110 DBY(020H)=P3 1130 CALL 6004H 1140 RETURN 2000 REM idle 2010 P3=255 : GOSUB 1100 2020 RETURN 3000 REM start 3010 P3=0EFH : GOSUB 1100 3015 P3=0CFH : GOSUB 1100 3020 RETURN 3100 REM repeated start 3110 P3=0DFH : GOSUB 1100 3115 P3=0FFH : GOSUB 1100 3116 P3=0EFH : GOSUB 1100 3117 P3=0CFH : GOSUB 1100 3120 RETURN 4000 REM stop 4010 P3=0CFH : GOSUB 1100 4012 P3=0EFH : GOSUB 1100 4015 P3=0FFH : GOSUB 1100 4020 RETURN 5000 REM get ack 5010 P3=0CFH : GOSUB 1100 5020 P3=0DFH : GOSUB 1100 5030 P3=0FFH : GOSUB 1100 5040 GOSUB 1000 5045 A=P3.AND.16 5050 P3=0DFH : GOSUB 1100 5060 P3=0CFH : GOSUB 1100 5070 RETURN 6000 REM send BY, get ack to A 6010 FOR I=1 TO 8 6020 BT=BY.AND.128 6025 BY=BY*2 6030 BT=BT/8 6040 P3=0CFH.OR.BT 6045 GOSUB 1100 6050 P3=0EFH.OR.BT 6055 GOSUB 1100 6060 P3=0CFH.OR.BT 6065 GOSUB 1100 6070 NEXT I 6080 GOSUB 5000 6090 RETURN 7000 REM read BY 7010 BY=0 7015 P3=0DFH : GOSUB 1100 7020 FOR I=1 TO 8 7035 P3=0FFH : GOSUB 1100 7040 GOSUB 1000 : BT=P3.AND.16 7045 P3=0DFH : GOSUB 1100 7050 BT=BT/16 7060 BY=BY*2+BT 7070 NEXT I 7080 RETURN 8000 REM send ACK 8010 P3=0CFH : GOSUB 1100 8020 P3=0EFH : GOSUB 1100 8030 P3=0CFH : GOSUB 1100 8040 RETURN 9000 REM send NAK 9010 P3=0DFH : GOSUB 1100 9020 P3=0FFH : GOSUB 1100 9030 P3=0DFH : GOSUB 1100 9040 RETURN 10000 REM build PORT3 access functions 10010 XBY(6000H)=085H : XBY(6001H)=0B0H : XBY(6002H)=020H : XBY(6003H)=022H 10020 XBY(6004H)=085H : XBY(6005H)=020H : XBY(6006H)=0B0H : XBY(6007H)=022H 10030 RETURN
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