
PSB 7280
Semiconductor Group
28
Data Sheet 1998-07-01
Channels
3.1.3
The parallel host interface can be selected to be either of the
(1) Motorola type with control signals CS,R/W, DS
(2) Siemens/Intel demultiplexed bus type with control signals CS, WR, RD
(3) or of the Siemens/Intel multiplexed address/data bus type with control signals CS,
WR, RD, ALE
The selection is performed via pin ALE as follows:
ALE tied to
V
DD
→
(1)
ALE tied to
V
SS
→
(2)
Edge on ALE
→
(3)
The occurence of an edge on ALE, either positive or negative, at any time during the
operation immediately selects the multiplexed bus type. A return to one of the other is
possible only if a hardware reset is issued.
Parallel Host Interface
3.1.4
The external memory interface allows the connection of both program and data
memories to the PSB 7280. The access to either type of memory is determined by the
signals CPS and CDS, respectively. In standard applications, the external memory
interface used as a program memory interface is normally not needed, but is reserved
for development purposes.
The upper 32k half (8000
H
-FFFF
H
) of the address space is reserved for execution of
software from external memory.
For executing software in the lower address range 0000
H
-7FFF
H
, a control line EA
(External Access) determines whether program is fetched from internal or external
memory. Thus, in standard applications, the EA
line should always be “high”.
The DSP program execution can be controlled from the outside by loading the
PC-counter of the DSP via the parallel host interface.
External Memory Interface
Two Audio receive and transmit channels
Independently programmable on SR, ST,
DU or DD with programmable locations
(start at bit 1
…
512) and lengths
(1
…
32 bits) with respect to RFS/TFS.
Independently programmable on SR, ST,
DU or DD with programmable locations
(start at bit 1
…
512) and lengths
(1
…
256 bits) with respect to RFS/TFS.
Two HDLC receive and transmit channels