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SRAM memory banks
This provides the information about how to access the memory on the FB2503. The
FB2503 hardware divides every 8K bytes of memory into a memory bank. To access the
data in the memory, you have to assign a bank number. The memory bank number
starts from zero. The last memory bank number depends on the size of the memory
chip used on the FB2503. For example, if you use the 128K bytes memory chip, the
bank number would be in the range of 0 to 15.
The I/O port address of the bank select base port 84ch or 84dh, the following is the
format of the chip select and bank enable.
Register
I/O
Port D7 D6 D5 D4 D3 D2 D1 D0
Bank select 84ch
-
-
BNK5 BNK4
-
-
-
Sel1
Bank
select 84dh
-
-
-
BNK3 BNK2 BNK1 BNK0
SRAM Sel1
U23 0
Disable 1
Where:
Sel1 Select the SRAM CHIP’s
Bnk4~bnk5
Bank select bits, D0 is the LSB
NOTE: Bnk0 to Bnk5 are the memory bank select bits. For example, 128KB memory has
sixteen 8K-byte banks; so 4 bits (Bnk0 to Bnk3) are needed.
Example:
Select the 10th bank of the U23 on the FB2503. Using
128K*8, and the base port is &H84c.
100 base_port=&H84c
110 OUT base_port,&H00
120 base_port=&H84d
130 base_port=&H09
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