pcjs/devices/pc8080/rom/vt100

layout	title	permalink
page	DEC VT100 ROMs	/devices/pc8080/rom/vt100/

DEC VT100 ROMs

The DEC VT100 Terminal used four 2Kb ROMs to store the code used by its 8080 processor. Their combined contents are stored in VT100.json.

As Trammell Hudson's VT100 Page 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 dumps:

• E56: 23-061E2.bin
• E52: 23-032E2.bin
• E45: 23-033E2.bin
• E40: 23-034E2.bin

And sure enough, concatenating those four DEC ROM dumps produces a perfect match for Trammell Hudson's VT100.bin.

The VT100 also used one 2Kb character generator ROM, which is stored in 23-018E2.json.