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Moved VT100 ROMs into the PC8080 directory

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Jeff Parsons 2016-07-26 16:03:16 -07:00 • committed by Jeff Parsons
commit 5b376917e3
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37
devices/vt100/rom/README.md
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---
layout: page
title: VT100 ROMs
permalink: /devices/vt100/rom/
---
VT100 ROMs
----------
The VT100 used four 2Kb ROMs to store the code used by its 8080 processor.
Their combined contents are stored in [VT100.json](VT100.json).
As Trammell Hudson's [VT100 Page](https://trmm.net/VT100) explains:
There are four 8316E ROM chips for the 8080 CPU on the logic board. Since they are custom mask ROMs,
Digital was able to have a different chip-select bit pattern and avoided having separate NOT gates on the inputs.
Note that the schematic appears to be incorrect -- E56 is the low order, and E40 is the high order address bits.
He then describes the memory mapping as follows:
ROM chip CS1 (20) A11/CS2 (18) A12/CS3 (21) Mapped address
E40 H H H 0x1800
E45 H L H 0x1000
E52 H H L 0x0800
E56 H L L 0x0000
The above PCB chip locations correspond to the following [DEC ROM](/devices/roms/dec/) dumps:
* E56: [23-061E2.bin](https://web.archive.org/web/20140723115846/http://www.dunnington.u-net.com/public/DECROMs/23-061E2.bin)
* E52: [23-032E2.bin](https://web.archive.org/web/20140723115846/http://www.dunnington.u-net.com/public/DECROMs/23-032E2.bin)
* E45: [23-033E2.bin](https://web.archive.org/web/20140723115846/http://www.dunnington.u-net.com/public/DECROMs/23-033E2.bin)
* E40: [23-034E2.bin](https://web.archive.org/web/20140723115846/http://www.dunnington.u-net.com/public/DECROMs/23-034E2.bin)
And sure enough, concatenating those DEC ROM four dumps produces a perfect match for Trammell Hudson's
[VT100.bin](http://trmm.net/images/2/20/VT100.bin).
The VT100 also used one 2Kb character generator ROM, which is stored in [23-018E2.json](23-018E2.json).