
ISAC-SX
PEB 3086
Description of Functional Blocks
Data Sheet
37
2003-01-30
3.2.2
The 8-bit parallel microcontroller interface with address decoding on chip allows easy
and fast microcontroller access.
The parallel interface of the ISAC-SX provides three types of P buses which are
selected via pin ALE. The bus operation modes with corresponding pins are listed in
Table 5
.
Parallel Microcontroller Interface
The occurrence of an edge on ALE, either positive or negative, at any time during the
operation immediately selects the interface type (3). A return to one of the other interface
types is possible only if a hardware reset is issued.
Note: If the multiplexed address/data bus type (3) is selected, the unused address pins
A0-A7 must be tied to
V
DD
.
A read/write access to the ISAC-SX registers can be done in
multiplexed or non-
multiplexed
mode:
In non-multiplexed mode the register address must be applied to the address bus (A0-
A7) for the data access via the data bus (AD0-AD7).
In multiplexed mode the address on the address/data bus (AD0-AD7) is latched in by
ALE before a data read/write access via the same bus is performed.
The ISAC-SX provides two different ways to address the register contents which is
selected with the AMOD pin (’0’ = direct mode, ’1’ = indirect mode).
Figure 7
illustrates
both register addressing modes.
Direct address mode
(AMOD = ’0’): The register address to be read or written is directly
set in the way described above.
Indirect address mode
(AMOD = ’1’): Only the LSB of the address is used to select
either the address register (A0 = ’0’) or the data register (A0 = ’1’). The microcontroller
writes the register address to the ADDRESS register before it reads/writes data from/to
the corresponding DATA register.
In indirect address mode the ISAC-SX evaluates no address line except the least
significant address bit. The remaining address lines must not be left open but have to be
tied to logical ’1’.
Table 5
Bus Operation Modes
Bus Mode
Motorola
Siemens/Intel non-multiplexed
Siemens/Intel multiplexed
Pin ALE
V
DD
V
SS
Edge
Control Pins
CS, R/W, DS
CS, WR, RD
CS, WR, RD, ALE
(1)
(2)
(3)