a E i - Commodore Is Awesome

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• 240V Fig 4 50 BS=INKEYS 60 IF /3S' -13$::PRIN I #1,BS; ' 70 GOT() 30 T Both H E programs N check first for a character P R from I the RS232 port, If one is Nfound, T it is output to the screen, If not, the program checks for a keyboard input. If found, the character is sent to the screen and also to the RS232. Another interesting experiment when using an IBM compatible machine is to make the following change to the mini terminal program on the Commodore: 60 IF 13$"" THEN PRINTE2,K Fig 5 Fig 6 MAINS A V ADAPTOR OATICRY Obviously, not many of you have access to an IBM, but this experiment does show up one very important problem with the Commodore's 3-line RS232 interface. If you take control of the IBM using the CTTY COM I command again and type DIR which is the MSDOS command to display the directory, the first few lines are printed normally and then suddenly, there is a whole lot of garbage. If you slow down the baud rates to say 300. the problem CUM NTER PAC Si Sin Soktt CND S': S GAD sONO T T LEVEL L L O G I C 145232,423 LLVEL LINE zATE , CTS V 0 - 0100ES IN4002 CI 2 ELECTROLYTIC 22eauf 25V 141-2r RESISTORS 4E7 ICI TAOS lA REGULATOR IC2 TTIO5 IA REGULATOR Ti 240V TO 8V0-6V TRANSFORMER SV V RS232 and run it. Now type the following on the IBM while in DOS: MODE COM 1: 1200,N,8,1 CITY COM I (MODE is external so disk containing the command must be in the default drive). This causes the IBM to think that its input/output device is the RS232 port instead of the console. This has the very odd effect of making the Commodore control the IBM! (although the character sets are different and some odd graphics characters may be printed). To return control to the IBM console, you must type CTTY CON on the Commodore. e V 014 • DIODES 1414002 CI • CAPACITOR ItIORE 25V 10r 2005 IA REGULATOR AI RESISTOR 4E7 may disappear. Why does this happen? Remember what I said about the Receive buffer? Well what happens is that data is received transparently over the RS232 lines and placed in the buffer. The buffer fills up quicker than Basic can empty it with the result that the buffer overflows and data is lost. Buffer overflow can be detectd by examining the ST status variable, but Basic is just too slow and you may still loose data, IBM COMPATAOLE ARC OR SIMILAR MACIDN IBM LISES n WAY BSC USES 5 PIN DIN YOUR COMMODORE January 1987 86 Solutions There are a few ways of solving this problem: I. Use a slower baud rate to let Basic keep up. 2. Devise some form of software data flow control. 3. Connect control lines up and use an x-line interface. 4. Use machine code to process RS232 data. Option 1 is not a good idea. Anyone who has used an RS 232 link at 300 baud will know why (yawn!), Option 2 is better but requires programming which we will touch on later when we discuss file transfer. Option 3 is not really practical here. Option 4 is probably the best solution in this case, Data can be removed from the buffer much faster using machine code and this will be fine for the speeds at which we will be working (up to 1200 baud). A very short machine code program can be written to handle E he RS232 interface. The routine that follows is given in the form of a Basic loader, Change the variable AD to any free area in your computer's memory (the tape buffer is a good place). This program is for a Cl28 but it should work on any of the Commodore machines discussed. 10 OPEN 2,2.0,CHRS(24)+CHRS(0) 11 REM PLUS4 USERS: OPEN 2 , 20 AD=2816:CA=AD 30 READ BY 2 40 , IF BY T H E N POKE AD,BY:AD= AD4-1:GOTO 30 50 0 : 60 , PRINT CHRS(14):REM SWITCH TO C LOWERCASE' 70 H SYS CA 80 90 R : $ 100 ( DATA 162,2,32,198,25532,228,255, 168 110 2 DATA 32 255 . 4 120 2 ) DATA 32,228,255,240,233,72, 16.2,2.32 0 + 130 4 C DATA 201,255,104,32,210,255. 32,204 , H 140 DATA 255,56,176,217,-1 255.152. R The only way out of this program is a 2403,32, SRUNSTOP/RESTORE. Table 3 is the 210, ( disassembled code with comments (addresses 5 may differ from your version. )
ing this let Basic ire data I use an RS232 idea. !link at 11). es prom later actical •: best an be faster 'ill be vill be code le the that Basic u any mory This ould (lore 401 'EN KE CH 55, 10, is is ts ir OBOO LDX #$02 01302 JSR SFEC6 OB05 JSR $FFE4 0808 TAY 01409 JSR $FFCC 01-10C TYA OBOD BEQ $0812 OBOF JSE $EFD2 0812 JSR $1 701315 BEQ $0B00 1- OBI 7 PHA; Save data 013I8 7 LDX #$02 OBIA JSR $FFC9 OH E4IL) PLA OBI E JSR HEED2 0821 JSR $FFCC 0824 SEC 0B25 BCS $01300 Table 3 The program uses the kernal jumptable calls so it should be valid for all of the machines. After the machine code has been placed in memory, the RS232 channel is opened with a file number of 2 (the channel number. If you change this Table 4 LDA #$02 LDX #$02 LDY #$00 JSR $FEBA LDA L$01 LDX if NAME LDY # NAME JSR $FEBD JSR SEFC0 Rest of code Character set translation All this should be fine for Commodore to Commodore communications. It will also work with Commodore to IBM/BBC etc. comms but may yield strange results, the reason being that the Commodores do not use standard ASCII codes. They use what is sometimes called PETSCII, the Commodore PET being the first to use it. The most noticeable effect of this is that certain characters will appear on the Commodore's screen as graphics characters. The solution to this is to insert some form of translation table or routine into the code. Since data RS232 ; Make channel 2 the current input device ; Scan the RS232 buffer for I character ; Save data ; Clear the channel ; Restore the date ; If data is a null (a zero byte) then skip ; Output valid character ; Check for keyboard input ; If none then recheck RS232 ; Make channel 2 the current output device ; Restore data : Send byte to RS232 ; Clear channel ; Force loop to check RS232 input you must change the two LDX instructions in the code) and the machine code routine called. Now the RS232 receive buffer does not get a chance to fill up so no data is lost. The OPEN statement could be replaced by the code in Table 4. ; Channel 2 ; Device 2 ; Secondary Addr. 0 ; Set logical file ; 2 chars in filename ; Pointer to filename ; Pointer to filename ; Set filename ; Open RS232 ,NAME:#B:24,0 ; Control and command register values (PLUS 4--- .NAME:#13:24,5) (#13: Is the byte directive of my C64 and C128 assemblers) flows two ways, a routine or table would be required for each of input and output. Two translation tables, each of 256 bytes, are required to handle outgoing and incoming data translations. The following program builds the translation tables and the machine code into memory starting at address AD. It needs at least 600 bytes to operate in so you need only change AD to the address you require. This version is for the Cl28 (Program Translate). Program Translate Line 5: AD=start address: BR=Control reg: CR=command reg. Y O U R COMMODOREjanuary1987 87 Lines 10-100: Prepare tables Lines 111-113: Setup name of channel (register images) Lines 120-160: POKE receive table Lines 170-200: POKE transmit table Lines 210-230: POKE code to memory Lines 240-270: Adjust table references in code Lines 280-290: Adjust register image references in code Lines 300-310: Select lowercase and call routine Lines 330-370: Code data Table 5 shows the disassembled machine code (addresses are offsets from the start address): Basically, the operation is the same as before except: 1. The channel is opened from machine code. 2. Characters sent and received are translated. Note that the backslash (\) character received will be displayed as a pound sign. The CBM Charset does not have a backslash. Transferring files via RS232 This is probably the most useful application of RS232; transferring data between unalike machines. It is possible to transfer programs between two entirely different machines. When using a 3-line interface, it is necessary to introduce some form of protocol into the software at both ends. This ensures that each machine understands exactly what the other intends to do. A typical protocol exchange would look like a conversation between the two machines: machine I: Are you there? machine 2: Yes. machine 1: Requesting data transfer. machine 2: OK, machine 1: Transferring data (block of data sent) machine 2: Received data. and so on. The "are you there", "yes" etc. messages are actually I byte control codes. Normal ASCII has 32 control codes (codes 0-31). The actual usage varies from system to system and there are one or tvvo protocol standards. For your own use, you don't have to follow any set protocol AS LONG AS BOTH MACHINES ARE USING
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