107 lines
4.9 KiB
Markdown
107 lines
4.9 KiB
Markdown
---
|
|
layout: page
|
|
title: VT100 Terminal
|
|
permalink: /devices/pc8080/machine/vt100/
|
|
machines:
|
|
- type: pc8080
|
|
id: vt100
|
|
debugger: true
|
|
---
|
|
|
|
VT100 Terminal
|
|
--------------
|
|
|
|
This is where we'll be testing another 8080-based machine: the VT100 Terminal. Unlike other VT100 emulations,
|
|
this will simulate a VT100 by running the terminal's original firmware inside the [PC8080](/modules/pc8080/) CPU emulator.
|
|
|
|
{% include machine.html id="vt100" %}
|
|
|
|
VT100 Memory Usage
|
|
------------------
|
|
|
|
As described in the [Technical Manual (July 1982)](http://bitsavers.informatik.uni-stuttgart.de/pdf/dec/terminal/vt100/EK-VT100-TM-003_VT100_Technical_Manual_Jul82.pdf),
|
|
p. 4-15, 8Kb (0x2000) of ROM is located at 0x0000, and 3Kb (0x0C00) of RAM immediately follows it at 0x2000. The ROM at
|
|
0x0000 contains all the VT100's 8080 code. The VT100 also contains a 2Kb character generator ROM, but that ROM is not
|
|
addressable by the CPU; it is used directly by the Video Processor.
|
|
|
|
[vt100romhax](http://vt100romhax.tumblr.com/post/90697428973/the-vt100-memory-map-and-8080-disassembly)
|
|
(aka [phooky](https://github.com/phooky)) further explains VT100 memory usage:
|
|
|
|
Start End Size Description
|
|
0x0000 0x1fff 8K Basic ROM
|
|
0x2000 0x2012 18B Blank lines for refresh (6 x 3B)
|
|
0x2012 0x204f 61B Stack area (grows down from 0x204e)
|
|
0x204f 0x22d0 641B Scratch Pad/Setup Area(?)
|
|
0x22d0 0x2c00 2352B Screen RAM
|
|
|
|
VT100 I/O Ports
|
|
---------------
|
|
|
|
From p. 4-17 of the Technical Manual:
|
|
|
|
READ OR WRITE
|
|
00H PUSART data bus
|
|
01H PUSART command port
|
|
|
|
WRITE ONLY (Decoded with I/O WR L)
|
|
02H Baud rate generator
|
|
42H Brightness D/A latch
|
|
62H NVR latch
|
|
82H Keyboard UART data input
|
|
A2H Video processor DC012
|
|
C2H Video processor DC011
|
|
E2H Graphics port
|
|
|
|
READ ONLY (Decoded with I/O RD L)
|
|
22H Modem buffer
|
|
42H Flags buffer
|
|
82H Keyboard UART data output
|
|
|
|
The PC8080 ChipSet component deals with the ER1400's Non-volatile RAM (NVR) ports, while the Keyboard component
|
|
deals with the Keyboard UART ports.
|
|
|
|
VT100 Video Processor
|
|
---------------------
|
|
|
|
Normally, the PC8080 Video component allocates its own video buffer, based on the specified buffer address
|
|
(*bufferAddr*) and other dimensions (eg, *bufferCols* and *bufferRows*), but the VT100 is a little unusual:
|
|
it has a custom Video Processor that uses DMA to request character data from any region of RAM, one line at a time.
|
|
It always defaults to address 0x2000 for the first line of character data, but each line terminates with 3 bytes
|
|
containing the attributes and address of the next line, so the location of subsequent lines will vary, depending
|
|
on the type of line:
|
|
|
|
- Single-wide characters (80 or 132 columns)
|
|
- Double-wide characters (40 or 66 columns)
|
|
|
|
In addition to single-wide vs. double-wide, line attributes can also specify double-high, along with whether the
|
|
top or bottom halves of the double-high characters should be displayed, because double-high always implies double-wide
|
|
(ie, there is no support for double-high, single-wide characters).
|
|
|
|
Conssequently, a VT100 [machine XML file](machine.xml) must set the Video component's *bufferRAM* property
|
|
to "true", indicating that existing RAM should be used, and a new property, *bufferFormat* must be set to "vt100",
|
|
enabling support for the VT100's line data format; eg:
|
|
|
|
<ram id="ram" addr="0x2000" size="0x0C00"/>
|
|
<video id="video" screenWidth="1600" screenHeight="960" bufferAddr="0x2000" bufferRAM="true" bufferFormat="vt100" bufferCols="80" bufferRows="24" ...>
|
|
|
|
VT100 Screen and Character Dimensions
|
|
-------------------------------------
|
|
|
|
Ordinarily, the VT100 screen displays 800 dots per horizontal scan, and a total of 240 horizontal scans, and by default,
|
|
it uses a 10x10 character cell, for a total of 80 columns and 24 rows of characters. However, in 132-column mode, it
|
|
uses a 9x10 character cell instead, implying a total of 1188 dots displayed per horizontal scan. This means we will have
|
|
to dynamically reallocate our internal buffers whenever the horizontal dimensions change. Also, if no AVO expansion
|
|
card is present, there is only enough RAM available for 14 rows of characters in 132-column mode.
|
|
|
|
For optimum scaling, I define the virtual screen size using multiples of the VT100's default "dot" dimensions; eg, 1600x960
|
|
(a horizontal multiplier of 2 and a vertical multiplier of 4). That gives us a virtual screen aspect ratio of 1.67.
|
|
|
|
According to the Technical Manual, a physical VT100 screen measures 12 inches diagonally, and in 80-column mode, characters
|
|
measure 2.0mm x 3.35mm (in 132-column mode, they measure 1.3mm x 3.35mm), which suggests that the text area of the screen is
|
|
roughly 160mm x 80mm, implying a screen aspect ratio of 2.0. However, after visually comparing the Technical Manual's SET-UP
|
|
screenshots to our test screens, 1.67 appears to be closer to reality than 2.0. I'll revisit this issue at a later date.
|
|
|
|
Additional VT100 Resources
|
|
--------------------------
|
|
|
|
[VT100 Publications](/pubs/dec/vt100/)
|