Yamaha V9938 Programmer's Manual page 15

1.4. Accessing the Video RAM (VRAM)
A video RAM of 128K bytes plus an expansion RAM of 64K bytes can be attached to
the VDP. Memory map is shown below.
(used for display)
To access memory, use the following procedure:
1. Switch respective bank (VRAM or expansion RAM)
2. Set the address counter A16 to A14
3. Set the address counter A7 to A0
4. Set the address counter A13 to A8, and specify if following data command will be
read or write
5. Read or write data to the memory
Step 1: Switching banks (VRAM to expansion RAM)
Applications are used to work with Video RAM, thus re-specification of the bank is
rarely necessary. It will be required if your application will need to access expansion RAM.
After performing necessary operations on expansion RAM, ensure that you map the Video
RAM back.
MSB
Register #45
© 1985 ASCII CORP. / NIPPON GAKKI CO.
Video RAM
7 6 5
0 MXC MXD MXS
0: Video RAM
1: Expansion RAM
Address
1FFFFh
↑
↑
↑
↑
10000h
0FFFFh
↑
↑
↑
↑
00000h
Expansion RAM
(for data I/O
registers)
4 3 2
DIY DIX
Page 15 of 108
1 0 LSB
EQ MAJ Argument
register
(ARG)
© 2010-2015 Eugeny Brychkov