Msg: 5416 *Conference*
09-12-94 23:46:50
From: COMET _
To : ANTHONY FEST
Subj: REPLY TO MSG #5396 (PRINTERS)
Parallel printers are just as popular as ever; many printers have BOTH a serial and parallel port. A print-buffer (external) can work with ANY computer that follows the Centronics parallel standard or the RS-232C serial standard (otherwise, some cabling is required). You are correct in surmising that you cannot use your modem AND serial port on the Model T simultaneously; both the internal modem and the serial port use the same UART (Universal Asynchronous Receiver/Transmitter chip. The purpose of the UART is to convert the serial start, data, parity, and stop bits to parallel data verifying proper code transmission, parity, and stop bits (for the receiver function.) The UART also converts data from parallel to series (for the transmitter function.) This is necessary since the CPU (and other chips) operate on 8 bits at a time, and the modem (and serial port) send/receive data a single bit at a time. You can see why the parallel transmission scheme hasn't gone out of style (although it has to have a thicker cable). Using an external parallel-to-series printer buffer, as I do, allows one to use the parallel port of the Model T to drive a seriial device, such as a CRT. Indeed, I do get 80 columns output whenever I "print" from the Model T. (Or 132 columns, if I set my VT320 in that mode.) I am using a Practical Peripherals Mini P/S 512 for this purpose.