Programming The Registers - Zenith Z-100 Reference Manual

The other eighteen registers are selected by the pointer information in the address
register. Then the CPU directs the information at address 3DS to be loaded into
the selected register. Transfers of address and parameter information to and from
the registers is via data lines DO through D7.

Programming the Registers

Programming Sequence
In general, you should observe the following sequence when selecting operating
parameters for the video interface.
Determine desired mode of operation, text mode or pixel addressable
graphics.
2. R e set video enable bit Also reset video override bit 0 in port address 3DA
if not already reset.
3. Pr o gram the CRT controller to desired mode.
4. De t ermine desired submode(s), then program mode and color select regis-
ters.
5. S e t video enable bit Also, set the video override bit, if desired.
Table 7.7 defines the individual registers in terms of values contained in them
and the results obtained with these values. All values are expressed in hexadecimal.
Video Graphics Programming
Page 7.19