mak kini:
I am not really in a position to tell you how you to design your printer interface. What does strike me though is that in order for the interface to work correctly and allow the microcontroller to synchronize with the printer, to send data to it at times the printer is ready, and to be aware when the printer of offline, out of paper etc etc, it is necessary to implement the support for the full capabilities of the interface. It is when you take a shortcut that you then do not get the benefit of the features that the interface provides. So.....I guess you will have to study that out and find the best solution.

Please be aware that if you try to use time delays in software to throttle the normal character flow to the printer buffer, then that delay will not be long enough for cases where the printer goes off to move the platten or the carriage. Printers have a lot of mechanically induced latency and even an 8052 can quickly fill a printer buffer to capacity where it then becomes necessary to wait for the print mechanism. If you try to design in software delays to take care of the worst case printer latency then you will severly impact your average printing speed to something way slower that what the printer can handle.

If you have your heart set on interfacing the printer logic via an I²C interface to the microcontroller I could suggest three possible alternatives for you.

A) Look at replacing the PCF8574 chip with a small CPLD programmed to provide slave mode I²C on one side and implement the printer interface on the other side. This scheme should cost very little more than the 8574 chip.

B) Another scheme would be to look at the lowest end small microcontrollers from Philips. They have internal FLASH and one could easily be porogrammed up as a custom I²C peripheral to interface your ptinter.

C) Look at a different Philips I²C bus port expander. For example the PCA9555 in a SSOP24 package offers 16 bits of I/O with an interrupt line capability. Another part is the PCF8575C which offers a 16 bit quasi-bidirectional port that functions not all unlike the ports on an 8051 part operate. This latter part is also in a small SSOP24 package.

Good Luck
Michael Karas