C511 datasheet(26/43 Pages) SIEMENS

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Semiconductor Group

C511 / C513

Additional On-Chip XRAM (not available in the C511/C511A/C513)

The C513A/C513A-H contain another 256 byte of on-chip RAM additional to the 256 byte internal

RAM. This RAM is called XRAM (‘eXtended RAM’).

The additional on-chip XRAM is logically located in the external data memory range from address

FF00H to FFFFH. The contents of the XRAM are not affected by a reset. After power up the content

is undefined, while it remains unchanged during and after reset as long as the power supply is not

turned off. The XRAM is controlled by SFR SYSCON as shown in table 11.

Table 11

Control of the XRAM

The XRAM is accessed as external data memory. Therefore, MOVX instruction types must be used

for accessing the XRAM. A general overview gives table 12.

Table 12

Accessing the XRAM

SFR SYSCON

Bit XMAP

Description

Reset value. Access to XRAM is disabled.

XRAM enabled. The signals RD and WR are not activated during MOVX

accesses in the XRAM address range.

Instruction

using

Instruction

Remarks

DPTR

(16-bit addr.)

MOVX A @DPTR

MOVX @DPTR,A

Normally the use of these instructions would use a

physically external memory. However, in the C513A/

C513A-H the XRAM is accessed if it is enabled by bit

XMAP and the 16-bit address (DPTR) is within the

XRAM address range FF00H - FFFFH.

R0/R1

(8-bit addr.)

MOVX A, @Ri

MOVX @Ri,A

If XRAM is enabled in the C513A/C513A-H, MOVX

instructions using Ri will always access the internal

XRAM. External data memory cycles will not be

generated in this case. If the XRAM is disabled, MOVX

instructions using Ri will generate normal external data

memory cycles.

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