PSB7238 SIEMENS [Siemens Semiconductor Group], PSB7238 Datasheet - Page 28

• Manufacturer Part Number: PSB7238
• Description: Joint Audio Decoder-Encoder - Multimode
• Manufacturer: SIEMENS [Siemens Semiconductor Group]

Semiconductor Group
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,
The selection is performed via pin ALE as follows:
ALE tied to
ALE tied to
Edge on ALE
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.
3.1.4
The external memory interface allows the connection of both program and data
memories to the PSB 7238. 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
software from external memory.
For executing software in the lower address range 0000
(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.
The external memory interface implements:
– protection against reading the internal ROM.
WR, RD, ALE
Parallel Host Interface
External Memory Interface
V
V
DD
SS
(3)
(2)
(1)
H
- FFFF
H
) of the address space is reserved for execution of
28
Interfaces and Memory Organization
H
- 7FFF
Data Sheet 1998-07-01
H
, a control line EA
PSB 7238