C511_1 Datasheet, PDF (31/128 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

External Bus Interface
can be enabled/disabled dynamically, it is also possible to enable ALE only when external memory
is accessed. This can be useful, if the external memory is accessed very seldom only.
4.4 XRAM Access Enable (SAB-C513A/A-H only)
The SAB-C513A/A-H maps 256 bytes of the external data space into the on-chip XRAM. Especially
when using the 8-bit addressing modes this could prevent access to the external memory extension
and might induce problems when porting software. Therefore it is possible to enable and disable the
on-chip XRAM. When the XRAM is disabled (default after reset) all accesses will go to the external
memory/IO.
Special Function Registers SYSCON (Address B1H)
MSB
Bit No. 7
6
5
4
3
2
B1H
1
0 EALE –
0
–
LSB
1
0
– XMAP SYSCON
Bit
–
7, 6, 3
XMAP
EALE
Function
Not implemented. Reserved for future use.
Reserved bits; these bits must be always written with the values
shown above.
Enable XRAM (SAB-C513A/A-H only).
XMAP=0 : XRAM disabled.
XMAP=1 : XRAM enabled.
Note: This bit is don’t care for the other members of the
SAB-C511/513 family, but should be written with “0“ for
compatibility reasons when writing to the SYSCON
register. When reading the bit in non-SAB-C513A
versions, it will be undefined.
Enable ALE generation.
If EALE=0, ALE signal will not be generated.
If EALE=1, ALE signal will be generated.
Reset Value (C513/513A/A-H) : 101X0XX0B
Reset Value (C511/C511A/C513) : 101X0XXXB
4.5 Overlapping External Data and Program Memory Spaces
In some applications it is desirable to execute a program from the same physical memory that is
used for storing data. In the SAB-C511/C513 the external program and data memory spaces can be
combined by AND-ing PSEN and RD. A positive logic AND of these two signals produces an active
low read strobe that can be used for the combined physical memory. Since the PSEN cycle is faster
than the RD cycle, the external memory needs to be fast enough to adapt to the PSEN cycle.
Semiconductor Group
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