P83C524IFA datasheet(14/76 Pages) PHILIPS

14 / 76 page

1997 Dec 15

Philips Semiconductors

Product speciﬁcation

8-bit microcontrollers

P83C524; P80C528; P83C528

Table 2

Internal and external program memory access with security bit set

INSTRUCTION

ACCESS TO INTERNAL

PROGRAM MEMORY

ACCESS TO EXTERNAL

PROGRAM MEMORY

MOVC in internal program memory

YES

MOVC in external program memory

YES

9.2

Internal Data Memory

The internal data memory is divided into three physically

separated parts: 256 byte of RAM, 256 byte of AUX-RAM,

and a 128 byte special function area (SFR). These parts

can be addressed as follows (see Table 3 and Fig.11):

• RAM 0 to 127 can be addressed directly and indirectly

as in the 80C51. Address pointers are R0 and R1 of the

selected register bank.

• RAM 128 to 255 can only be addressed indirectly.

Address pointers are R0 and R1 of the selected register

bank.

• AUX-RAM 0 to 255 is indirectly addressable as the

external data memory locations 0 to 255 with the MOVX

instructions. Address pointers are R0 and R1 of the

selected register bank and DPTR. When executing from

internal program memory, an access to AUX-RAM 0 to

255 will not affect the ports P0, P2, P3.6 and P3.7.

• the SFRs can only be addressed directly in the address

range from 128 to 255.

An access to external data memory locations higher than

255 will be performed with the MOVX DPTR instructions in

the same way as in the 80C51 structure, i.e. with P0 and

P2 as data/address bus and P3.6 and P3.7 as write and

read timing signals (see Figures 7, 8, 9 and 10). Note that

the external data memory cannot be accessed with R0 and

R1 as address pointer.

Fig.11 shows the internal and external data memory

address space. Fig.12 shows the Special Function

occupy locations 0 through 31 in the lower RAM area. Only

one of these banks may be enabled at a time. The next 16

bytes, locations 32 through 47, contain 128 directly

addressable bit locations.

The stack can be located anywhere in the internal 256 byte

RAM. The stack depth is only limited by the available

internal RAM space of 256 bytes. All registers except the

Program Counter and the four 8-bit register banks reside

in the SFR address space.

Table 3

Internal data memory access

LOCATION

ADDRESSED

RAM 0 to 127

DIRECT and INDIRECT

RAM 128 to 255

INDIRECT only

AUX-RAM 0 to 255

INDIRECT only with MOVX

Special Function Register (SFR) 128 to 255

DIRECT only

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