Zenith Data Systems Z-100 Series - Status Register; Quick Reference Charts; Register Addresses

Page 4.9
Software Considerations
Status Register
The status register is a 4-bit, read-only register located at I/O port 3BAH.
Bit 0 is the horizontal drive signal, bits 1 and 2 are the font number in
use, and bit 3 is the video data. The programmer can look at bits 1 and
2 for font information and can use bits 0 and 3 for diagnostics, but data
bits 0 and 3 are read "on the fly". These data bits may not meet the
timing requirements
to be read properly.
Quick Reference Charts
The following tables give the addresses and default values for the registers
accessible
to the programmer. Table 4.5 shows all the addresses which
can be written to or read from and their use. Table 4.6 shows the CRTC
registers and their default values.
Table 4.5. Register Addresses
1/0
ADDRESS
384
385
388
38A
FUNCTION
CRTC Index
Register
CRTC Data
Register
CRT Control
Register
CRT Status
Port
DESCRIPTION
Used to select a CRTC register to write to. This register
must be written
to before data can be entered into
the CRTC registers.
Data written into this register
is loaded into the CRTC
register selected by writing into address 384.
This register controls the functions of the card includ-
ing communication, video display, the page of the dis-
play, blink enable, and font selection. The function of
these bits
is shown in Table 4.1.
This port allows the programmer to look at the font
selected, the video data, and the horizontal sync.