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Posted by Tomi Engdahl (195.197.151.211) on December 11, 2003 at 08:58:34:
In Reply to: centronics adapter posted by karthikbalaguru on December 11, 2003 at 08:44:14:
: Could anyone point me the centronics adapter schematics
: for 8051 and 80column epson Printer communication ?
For basic communications with centronics printer you might not need any fancy schematic at all.
With several I/O-lines (8 for data, few handshake lines out, few handshake lines in) and some software to do the handshaking, and that should do it. Your 8051 should have enough I/O pins to do the job. The centronics interface uses TTL level logic signals, as does 8051. So direct interfacing should work in laboratory systems (maybe adding some ESD protection and EMC filtering components would be a good idea in real life product).
A typical 8051 contains CPU with boolean processor, 5 or 6 interrupts, 2 or 3 16-bit timer/counters, programmable full-duplex serial port, 32 I/O lines, RAM and ROM/EPROM in some models.
Here is the idea for the program to write characters to Centronics line
1. Read one character to send to printer port from your software data sening buffer
2. Set the Centronics data bits to present the character (usually write the charaxcter value to I/O port or memory address that controls those 8 output pins used for data lines)
3. Wait few microseconds
4. Activate strobe line
5. Wait for for about 10-100 microseconds
6. Deactivate strobe line
7. Wait that ACKNOWLEDGE input line is actiavted by printer
8. Wait that ACKNOWLEDGE input line is deactivated by the printer
9. Go to step 1 to send the next character out
This is how basic Centronics communications works.
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