p87lpc778 NXP Semiconductors, p87lpc778 Datasheet - Page 66

• Manufacturer Part Number: p87lpc778
• Description: Cmos Single-chip 8-bit 80c51 Microcontroller 128-byte Data Ram, 8 Kb Otp
• Manufacturer: NXP Semiconductors

Philips Semiconductors
9397 750 12378
Product data
8.17.1 Software reset
8.17.2 Dual data pointers
8.18 EPROM characteristics
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.
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:
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 P87LPC778 since the part does
not have an external data bus. However, they may be used to access EPROM
configuration information (see
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.
Programming of the EPROM on the P87LPC778 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 P87LPC778 in an
application board.
The P87LPC778 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 P87LPC778 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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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.
Rev. 01 — 31 March 2004
Section 8.18 “EPROM
CMOS single-chip 8-bit microcontroller
characteristics”).
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
P87LPC778
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