C161U
Memory Organization
Preliminary Data Sheet
57
02.2000
PRELIMINARY
PRE
LI
M
INAR
Y
- E
XCE
RP
T
-
4.2
External Memory Space
The C161U is capable of using an address space of up to 2 MByte. Only parts of this
address space are occupied by internal memory areas. All addresses which are not used
for on-chip memory (RAM) or for registers may reference external memory locations.
This external memory is accessed via the C161U’s external bus interface.
Four memory bank sizes are supported:
Non-segmented mode: 64 KByte
with A15...A0 on PORT0 or PORT1
2-bit segmented mode: 256 KByte with A17...A16 on Port 4 and A15...A0 on PORT0 or PORT1
4-bit segmented mode: 1 MByte
with A19...A16 on Port 4 and A15...A0 on PORT0 or PORT1
8-bit segmented mode: 2 MByte
with A20...A16 on Port 4 and A15...A0 on PORT0 or PORT1
Each bank can be directly addressed via the address bus, while the programmable chip
select signals can be used to select various memory banks.
The C161U also supports four different bus types:
l
Multiplexed 16-bit Bus
with address and data on PORT0 (Default after Reset)
l
Multiplexed 8-bit Bus
with address and data on PORT0/P0L
l
Demultiplexed 16-bit Bus with address on PORT1 and data on PORT0
l
Demultiplexed 8-bit Bus
with address on PORT1 and data on P0L
Memory model and bus mode are selected during reset by pin EA and PORT0 pins. For
further details about the external bus configuration and control please refer to chapter
"The External Bus Interface".
External word and byte data can only be accessed via indirect or long 16-bit addressing
modes using one of the four DPP registers. There is no short addressing mode for
external operands. Any word data access is made to an even byte address.
For PEC data transfers the external memory can be accessed independent of the
contents of the DPP registers via the PEC source and destination pointers.
The external memory is not provided for single bit storage and therefore it is not bit
addressable.