C511 datasheet(31/128 Pages) SIEMENS

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Semiconductor Group

4-4

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)

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.

Bit

Function

–

Not implemented. Reserved for future use.

7, 6, 3

Reserved bits; these bits must be always written with the values

shown above.

XMAP

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

versions, it will be undefined.

EALE

Enable ALE generation.

If EALE=0, ALE signal will not be generated.

If EALE=1, ALE signal will be generated.

EALE

–

B1H

SYSCON

Bit No.

MSB

LSB

0–

–

XMAP

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