Xerox Memorywriter 645S
| General Info | |
|---|---|
| Release Year | 1985 |
| Manufacturer | Xerox |
| Condition | Working |
| Identifiers | |
| Model Number | 645S |
| Technical Specifications | |
| Software Environment | Proprietary DOS |
| CPU | 8088 |
| Memory Capacity | 64-128k |
| Memory Type | 64k with CPU, Add-in 64k RAM card |
| Removable Storage | 5.25" FDD |
| Graphics | 50Hz Monochrome TTL interlaced |
| Display Interface | MDA-like but not directly compatible |
| Power Requirements | |
| Input Voltage | 120V AC |
| QR Code | |
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The Xerox Memorywriter 600 Series of typewriters featured multiple different models with varying levels of Word Processing capabilities. At the top of the model line were the 645S and 645E. The 645S shown here features a display capable of working on documents with full asynchronous word processing features. Lower end models likely have a simple buffer shown on an internal display for making minor corrections and possibly the ability to store forms for re-printing.
The Xerox 600 Series uses an unusual backplane design with different add-in cards for features. Different models did not have features like the external CRT or floppy drives and are likely missing these cards. The 645E should also contain a card capable of some kind of networking with other Xerox systems at the time to double as a printer.
I would like to also specifically state, this machine doe not contain a Zilog Z80 of any kind. It's somewhat of an assumption that unusual 1980s machines would use Z80 CPUs and this machine already has multiple general purpose CPUs in it. But none of them are a Z80.
Repairs - Modifications
2024-01
- Replaced bearings in carriage drive motor after discovering they were no longer smooth
- Re-lubricated entire cable drive pulley set to allow carriage to move freely
- Determined correct belt size is 11in x 1/8in for Sugart SA200 floppy drives
Photos
Backplane Cards
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The primary CPU card for the machine. On the left side you can see a footprint for an internal battery and may notice the RAM IC above the CPU is SRAM. It's likely different configurations of the machine had the capability to store documents internally rather than exclusively on disks like this example.
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This board contains 64k of 4164 RAM ICs
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The floppy drive controller uses a WDC FD1793PL-02. It also has an 8085 on it which I haven't confirmed, but I suspect handles the keyboard interface.
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The CRTC uses a Hitachi HD46505SP. The video out is 50Hz interlaced for some reason and is fairly noticeable and unpleasant in person for high resolution monochrome text
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Mechanical interface card handles driving and signalling motors and solenoids.
Other PCBs
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This is a "Type Right" module that goes between the keyboard and system bus for checking spelling as the system is used. The word processing software on the base system disk is fully capable of spell checking, this module is only needed when working in "Printer" mode where you type directly to the paper.
