From 96560e5b8b806f5a3fb4fe37f25c0a09435b326f Mon Sep 17 00:00:00 2001 From: Jeff Parsons Date: Wed, 3 Aug 2016 13:57:09 -0700 Subject: [PATCH] Update VT100 machine README --- devices/pc8080/machine/vt100/README.md | 26 +++++++++++++++++++++++--- 1 file changed, 23 insertions(+), 3 deletions(-) diff --git a/devices/pc8080/machine/vt100/README.md b/devices/pc8080/machine/vt100/README.md index 8c6e3c546..a2972598e 100644 --- a/devices/pc8080/machine/vt100/README.md +++ b/devices/pc8080/machine/vt100/README.md @@ -25,7 +25,7 @@ p. 4-15, 8Kb (0x2000) of ROM is located at 0x0000, and 3Kb (0x0C00) of RAM immed 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: +(aka [phooky](https://github.com/phooky) aka Adam Mayer) further explains VT100 memory usage: Start End Size Description 0x0000 0x1fff 8K Basic ROM @@ -57,8 +57,28 @@ From p. 4-17 of the Technical Manual: 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. +The PC8080 ChipSet component deals with the ER1400's Non-volatile RAM (NVR) ports, the Flags buffer, and the +DC011 and DC012 circuits, while the Keyboard component deals with the Keyboard UART. + +You might wonder why the PC8080 Video component doesn't manage the DC011 and DC012. In fact, the above labels are misleading. +If you look at the Functional Diagram on p. 4-53 of the Technical Manual, you'll see that DC011 and DC012 are really +peripheral components providing inputs to the Video Processor. Moreover, they are not exclusive to the Video Processor. +For example, the LBA7 output of the DC011 is also used to clock the NVR chip. + +In most respects, the VT100 Technical Manual provides a phenomenal amount of detail. +However, documentation for some of the above ports is almost non-existent. It's only thanks to +[third parties](https://github.com/phooky/VT100-Hax/blob/master/Platform%20Notes.md) that we have, for example, the following +information about the Flags buffer (port 0x42): + + Bit Active? Description + 7 H KBD Transmit Buffer Empty + 6 H LBA 7(?) (It's a pin on the backplane connector...) - used to clock NVR - line buffer address + 5 H NVR DATA + 4 L EVEN FIELD (comes out of the video timing generator) + 3 H OPTION PRESENT (terminal output option???) + 2 L GRAPHICS FLAG (is VT52 graphics card present) [I think he meant VT125 -JP] + 1 L ADVANCED VIDEO (is AVO present) + 0 H XMIT FLAG VT100 Video Processor ---------------------