I am trying to figure out the Checksum alrorithm used by one of the printers I am working with. I have set up a serial communications monitoring interface and was able to record the "conversation" betwee the device and the printer. At the end of the every data line, sent to the printer, device sends a 16 bit code. I suspect the device and the printer use CRC-16 algorithm to calculate this code.
Example 1 of the "conversation":
--------------------------
1) Device:
4 4 0 4 48 227 86
2) Printer:
16 6
3)Device:
2 48 0 83 30 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 95 13 10 224 62
4) Printer:
16 21
As a result of this "Conversation" a Printer prints 83 underscore characters
--------------------------
Here is Example 2 of the recorded conversation:
1) Device:
4 4 0 4 48 227 86
2) Printer:
16 6
3) Device:
2 48 0 44 31 14 32 32 32 32 32 32 32 32 32 32 32 32 80 82 79 68 85 67 84 32 83 85 77 77 65 82 89 32 32 32 32 32 32 32 32 32 32 32 32 20 13 10 196 130
4) Printer:
16 21
As a result of this conversation, printer Prints “Product Summary” in the middle of the line
--------------------------
I have analized the strings sent by the device and here is what I've come up with.
2, 48, 0 - is likely to be a beginning of the printing command
44 (in exampe 2) and 83 (in example 1) - is likely to be the number of characters to be printed
[224 62] (in example 1) and [196 130] in example 2 is the checksum.
QUESTION:
Find the way to calculate this checksum.
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Have you actually tried the standard 16-bit CRC (CRC-CCITT1 [X.25])?
I have, and found no match even by skipping the first bytes one-by-one, and with/without the trailing CR/LF.
But to find out the algorithm, you should use an algorithmic way:
Print 1 byte, get the checksum for all printable characters.
Print 2 bytes, get the checksum for some fixed characters as the first byte and for all printable characters for the second byte.
Write us the results.
I wrote a little test program, which calculated checksums for all printable characters. Basically this code was sending characters to the printer, one at a time, and iterating through all possible combinations of the checksum. I even got the printer to print this way. It worked nicely but xtreeemly slow.
Here is the output of my program for some of the characters.
2, 48, 0, 1, 32,160, 98 -- This set of bytes sends a [space] character (32) to the printer
2, 48, 0, 1, 33,41, 115 -- This set of bytes sends a [!] character (33) to the printer
2, 48, 0, 1, 34,178, 65 -- This set of bytes sends a ["] character (34) to the printer
2, 48, 0, 1, 35,59, 80 -- This set of bytes sends a [#] character (35) to the printer
2, 48, 0, 1, 36,132, 36
2, 48, 0, 1, 37,13, 53
2, 48, 0, 1, 38,150, 7
2, 48, 0, 1, 39,31, 22
2, 48, 0, 1, 40,232, 238
I hope this helps :)
Dimitry, the printer that I am working with was manufactured by Fujitsu about 15 years ago... I tried to find any info about it on google without any luck.
I generated some more sample data. This time I was calculating a checksum for different number of zeros sent to the printer. Here are the results:
2, 48, 0, 1, 0, 162, 67
2, 48, 0, 2, 0, 0, 63, 105
2, 48, 0, 3, 0, 0, 0, 166, 213
2, 48, 0, 4, 0, 0, 0, 0, 53, 240
Here is another sample, which was generated for a 2 byte data, incrementing a second byte by one:
2, 48, 0, 2, 32, 0, 12, 74
2, 48, 0, 2, 32, 1, 133, 91
2, 48, 0, 2, 32, 2, 30, 105
2, 48, 0, 2, 32, 3, 151, 120
2, 48, 0, 2, 32, 4, 40, 12
Thank you.
This is the code. Output in Hex format, but it is correct.
#include <stdio.h>
unsigned char string1[] = { 2, 0x30, 0, 2, 0x20, 1 }; // 0x85, 0x5B };
unsigned char string2[] = { 2, 0x30, 0, 2, 0x20, 2 }; // 0x1E, 0x69 };
unsigned char string3[] = { 2, 48, 0, 44, 31, 14, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 80, 82, 79, 68, 85, 67, 84, 32, 83, 85, 77, 77, 65, 82, 89, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 20, 13, 10 }; // 0xC4, 0x82 };
unsigned long reflect(unsigned short crc, int bitnum)
{ // reflects the lower 'bitnum' bits of 'crc'
unsigned short i, j=1, crcout=0;
for(i=(unsigned short)1<<(bitnum-1); i; i>>=1) {
if(crc & i)
crcout |= j;
j <<= 1;
}
return( crcout );
}
unsigned short crcbitbybit(unsigned char *p, unsigned short len)
{ /* bit by bit algorithm with augmented zero bytes. */
unsigned short i, j, c, bit;
unsigned short crc = 0;
for(i=0; i<len; i++) {
c = (unsigned short)*p++;
c = reflect(c, 8);
for (j=0x80; j; j>>=1) {
bit = crc & 0x8000;
crc <<= 1;
if(c & j)
crc |= 1;
if(bit)
crc ^= 0x1021;
}
}
for(i=0; i < 16; i++) {
bit = crc & 0x8000;
crc <<= 1;
if(bit)
crc ^= 0x1021;
}
crc = reflect(crc, 16);
return(crc);
}
int main( void )
{
printf("Crc = 0x%x\n", crcbitbybit((unsigned char *)string1, sizeof(string1)));
printf("Crc = 0x%x\n", crcbitbybit((unsigned char *)string2, sizeof(string2)));
printf("Crc = 0x%x\n", crcbitbybit((unsigned char *)string3, sizeof(string3)));
}
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by: dimitryPosted on 2004-05-07 at 15:29:23ID: 11018964
Can you give more examples and printer name ?