Access Registers - Yamaha V9938 Programmer's Manual

MSB
R#19
VDP generates interrupt when it starts to display respective scan line if bit 4 "IE1" of
register R#0 is set to 1. Write a value to this register R#19, and when VDP will start
displaying the specified line, it will set bit 0 "FH" of status register S#1 to 1.

2.1.5. Access registers

Access registers is the set of registers used for accessing other VDP registers or VRAM.
These registers include R#14, R#15, R#16 and R#17.
MSB
R#14
R#14 contains three senior bits of VRAM access address. In all modes, except
GRAPHIC1, GRAPHIC2, MULTICOLOR and TEXT1, if there's a carry flag from A13 the value
in this register is automatically incremented.
MSB
R#15
R#15 points to the respective status register (S#0...S#9) to be read.
MSB
R#16
R#16 points to the respective color palette register (P#0...P#15) to be accessed.
MSB
R#17
R#17 is a register used in indirect access to other VDP registers. It also has auto-
increment flag (AII) which is used to control increment of value in this register.
© 1985 ASCII CORP. / NIPPON GAKKI CO.
7 6 5
IL7 IL6 IL5
7 6 5
0 0 0
7 6 5
0 0 0
7 6 5
0 0 0
7 6 5
AII 0 RS5
4 3 2
IL4 IL3 IL2
4 3 2
0 0 A16
4 3 2
0 S3 S2
4 3 2
0 C3 C2
4 3 2
RS4 RS3 RS2
Page 21 of 108
1 0 LSB
IL1 IL0 Interrupt line
register
1 0 LSB
A15 A14 VRAM access
base register
1 0 LSB
S1 S0 Status register
pointer
1 0 LSB
C1 C0 Color palette
address register
1 0 LSB
RS1 RS0 Control register
pointer
© 2010-2015 Eugeny Brychkov