Carel Vedder HRG1

This expansion, compatible with both American and Japanese Model1's and the Video Genie I, II, EG 3003 and EG 3008 produces a 184 * 192 monochrome screen. When installed, it displays on the original TRS-80 screen. All timing is derived fromthe TRS-80. The Video memory, 12 KByte Static RAM, is controlled via six I/O ports, 0 to 5.

Port usage:

Port 0 disables the HRG1, port 1 enables it. Port 4 reads six bits from the HRG1 memory, port 5 writes six bits to the HRG1. Port 2 and 3 are used to program addressing:

    |           port 2             |           port 3             |
bit: 0   1   2   3   4   5   6   7   0   1   2   3   4   5   6   7
    |     64 char. hor.    | 16 reg. vert. | 12 pnts. vert.|      |

The extension to Basic BASGR gives eight extra commands:

The Basic extension BASGR was written for NEWDOS80 V2.0, and loaded from 5200H. It then positions itself in hi memory.

The hardware:

The schema has some interesting non-technical details:
"© RB Electronic Gmbh" is a German company. So, Carel Vedder didn't design the HRG1 themselves
The Text above reads "Repair shop scheme, do not give away".

The HRG1 is connected to the TRS-80 with two flatcables: a 16 wire and a 24 wire cable. The HRG1 output is OR-ed with the original video signal.