Programming Considerations - NEC Advanced Personal Computer System Reference Manual

Controller PCB
DISPLAY
POSITION
1
CHARACTER-CODE
2
STORAGE
3
4
(LAST ADDRESS) 2000
CHARACTER-
ATTRIBUTE-CODE
STORAGE
DISPLAY
POSITION
1
2
3
4
(LAST ADDRESS) 2000
CHAR-CODE
T
CHAR-CODE '2'
I
CHAR-CODE 'Q'
CHAR-CODE 'F'
rCHAR-C~E
'A
l
C-A CODE 'OB'
C-A CODE 'VB'
C-A CODE 'UB'
C-A CODE 'BL'
~
l
[ C-A CODE 'RV'
~ Q
,-
I r-
VIDEO SCREEN
Figure 3-7 Relationship Between Character Code, Character-Attribute Code,
Display Position, and Video Screen
3.2.2 Programming Considerations
The G DC has four registers, all of which can be accessed directly or indirectly by the
8086 processor: status register, First-In First-Out (FIFO), command register, and
data register. The I/O addresses, functions, and bit maps are summarized in Table
3-2.
The status register is an 8-bit read-only register. Its I/O address is 80 (HEX). Using
the 8086 I/O In command, the status register can be read at any time.
Figure 3-8 is a bit map of the G DC status register. Table 3-3 describes the contents
of the status register.
3-8
II