IBM 5181 Compact Printer Signaling Through an RS232 Breakout Box
(Be sure to view this in high definition to clearly see the lights!) This is a demonstration of an IBM 5181 Compact Printer with the RS232 signaling visible using an RS232 breakout box. The printer is run by an embedded CPU that has a total of 4K of firmware and just 2176 bytes of RAM. The breakout box shows you some of how the RS232 signaling works, including the printer using the Clear to Send (CTS) light to implement hardware flow control, pausing the computer as needed so that it can move the carriage without dropping bytes.
More information about this printer is available at https://www.brutman.com/PCjr/pc_compa... .
(Small correction: the Hitachi can address up to 64KB of RAM. A 2KB SRAM chip can be found on the board under the printer mechanism.)