Editing IBM System/23 Datamaster (section)

== I/O and Peripherals ==

* '''Printers''' — up to '''two''' of the IBM '''5217''', '''5241''' or '''5242''' in any combination. The motherboard has one integrated printer port; an optional Printer Control Adapter card adds a second (diagnostic test 3A confirms its presence).<ref>Datapro M11-491-35.</ref>
* '''Communications''' — single Intel 8251 USART on the motherboard providing one async/sync serial channel. Often described as a "current-loop serial port". '''BSC''' (Binary Synchronous Communications) is supported as an optional feature.<ref>oldcomputers.net, "IBM 5322 System/23 Datamaster".</ref>
* '''Keyboard''' — '''83-key pre-Model F''', '''capacitive matrix''', '''Intel 8048''' microcontroller, parallel interface to the motherboard's 8255 PPI. Often cited as the '''earliest production Model F design''' (the IBM PC moved the keyboard to a serial interface but kept the same capacitive Model F mechanism). The 8048's firmware is unique to the Datamaster — '''replacement requires a known-good Datamaster keyboard'''; PC firmware is not interchangeable.
* '''Diagnostics probe port''' at the rear (driven by an 8255 in mode 0) — 8-bit data plus probe power, used by a service-engineer probe with LEDs to display the current POST test ID even when the CRT has not yet initialised.

[[File:IBM 5322 keyboard close up.jpg|center|thumb|480px|IBM 5322 Datamaster detached keyboard close-up — 83-key capacitive Model F predecessor with Intel 8048 microcontroller. (Image: Wikimedia Commons, Public domain)]]