Davong DSI-A16 Reference Manual

DSI-A16 OPERATING INSTRUCTIONS
> MEMORY MAP
The DSI-A16 card is a 16K byte device. However, this 16K is mapped into a 12K
address space (see fig.A). This is achieved by dividing the address space into two
banks of 4K and one bank of 8K. In addition, this 16K area is shared with the APPLE
ROM array.
ON BOARD
APPLE
-ROM
fig.A
The RAM may be selected for read only or for read and write. Also the DSI-A16
may be entirely disabled so that the ROM may be accessed, or it can be partially
enabled so that the RAM may be written and the ROM read.
To configure the DSI-A16 card, there are eight control addresses that the user
reads from. This reading action, in addition to causing a configuration change,
causes a Status nibble to be returned in the low 4 bits.
> CONTROL ADDRESSES
$C080 Reading this address disables the ROM and enables BANK2 and RAM1 for
read only. (The RAM is write protected. )
$C081 Reading this address twice consecutively enables ROM and write enables
BANK2 and RAM 1.
$CO82 Reading this address enables ROM and write protects RAM.
$C083 Reading this address twice consecutively enables BANK2 and RAM1 for
both read and write. )
$C088 Reading this address disables the ROM and enables BANK1 and RAM1 for
read only.
$C089 Reading this address twice consecutively write enables BANK1 and RAM1
and enables the ROM for read access.
$CO8A Reading this address enables the ROM and write protects the RAM.
$CO8B_ Reading this address twice consecutively enables BANK1 and RAM1 for
read and write.