P87LPC779FDH datasheet(61/74 Pages) PHILIPS

61 / 74 page

Philips Semiconductors

P87LPC779

CMOS single-chip 8-bit microcontroller

Product data

Rev. 02 — 03 May 2004

61 of 74

9397 750 13213

8.17.1

Software reset

The SRST bit in AUXR1 allows software the opportunity to reset the processor

completely, as if an external reset or Watchdog reset had occurred. If a value is

written to AUXR1 that contains a ‘1’ at bit position 3, all SFRs will be initialized and

execution will resume at program address 0000. Care should be taken when writing

to AUXR1 to avoid accidental software resets.

8.17.2

Dual data pointers

The dual Data Pointer (DPTR) adds to the ways in which the processor can specify

the address used with certain instructions. The DPS bit in the AUXR1 register selects

one of the two Data Pointers. The DPTR that is not currently selected is not

accessible to software unless the DPS bit is toggled.

Speciﬁc instructions affected by the Data Pointer selection are:

• INC DPTR: Increments the Data Pointer by 1.

• JMP @A+DPTR: Jump indirect relative to DPTR value.

• MOV DPTR, #data16: Load the Data Pointer with a 16-bit constant.

• MOVCA, @A+DPTR: Move code byte relative to DPTR to the accumulator.

• MOVXA, @DPTR: Move data byte the accumulator to data memory relative to

DPTR.

• MOVX @DPTR, A: Move data byte from data memory relative to DPTR to the

accumulator.

Also, any instruction that reads or manipulates the DPH and DPL registers (the upper

and lower bytes of the current DPTR) will be affected by the setting of DPS. The

MOVX instructions have limited application for the P87LPC779 since the part does

not have an external data bus. However, they may be used to access EPROM

conﬁguration information (see Section 8.18 “EPROM characteristics”).

Bit 2 of AUXR1 is permanently wired as a logic 0. This is so that the DPS bit may be

toggled (thereby switching Data Pointers) simply by incrementing the AUXR1 register,

without the possibility of inadvertently altering other bits in the register.

8.18 EPROM characteristics

Programming of the EPROM on the P87LPC779 is accomplished with a serial

programming method. Commands, addresses, and data are transmitted to and from

the device on two pins after programming mode is entered. Serial programming

allows easy implementation of in-circuit programming of the P87LPC779 in an

application board.

The P87LPC779 contains three signature bytes that can be read and used by an

EPROM programming system to identify the device. The signature bytes designate

the device as an P87LPC779 manufactured by Philips. The signature bytes may be

read by the user program at addresses FC30h, FC31h and FC60h with the MOVC

instruction, using the DPTR register for addressing.

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