We Control the Horizontal and Vertical!

A project log for ISA 8-Bit Video Experiments

A Series of Experiment to Create an ISA 8-Bit Video Card

Dave's Dev LabDave's Dev Lab 08/13/2019 at 01:070 Comments

The first of the MC6845 based video test boards is assembled and working! I am able to write to the registers on the 6845 to set both the horizontal and vertical timing which I was able to verify with my oscilloscope. Earlier in the week I installed Open-Watcom and setup an environment where i could compile DOS executables on my linux desktop. once that was working i created a simple iotool that allows me to read/write to port addresses from the DOS prompt. The original IBM designers left port 0x300 to 0x31F available for prototype cards, so i'm currently mapping the 6845's registers to 0x300 and 0x301 using a GAL16V8. after doing a series of tests, i'll order up the next board which include a Data ROM and a Character ROM.