p87c591vfb NXP Semiconductors, p87c591vfb Datasheet - Page 19

• Manufacturer Part Number: p87c591vfb
• Description: Single-chip 8-bit Microcontroller With Can Controller
• Manufacturer: NXP Semiconductors

Philips Semiconductors
7.4
The dual DPTR structure (see Figure 7) is a way by which
the chip will specify the address of an external data
memory location. There are two 16-bit DPTR registers that
address the external memory, and a single bit called DPS
= AUXR1/bit0 that allows the program code to switch
between them.
The DPS bit status should be saved by software when
switching between DPTR0 and DPTR1.
Note that bit 2 is not writable and is always read as a zero.
This allows the DPS bit to be quickly toggled simply by
executing an INC AUXR1 instruction without affecting the
other bits.
DPTR Instructions
The instructions that refer to DPTR refer to the data pointer
that is currently selected using the AUXR1/bit 0 register.
The six instructions that use the DPTR are as follows:
2000 Jul 26
handbook, full pagewidth
Single-chip 8-bit microcontroller with CAN controller
Dual DPTR
AUXR1
DPS
BT0
(83H)
DPH
(82H)
DPL
Fig.7 Dual DPTR:
DPTR1
DPTR0
19
The data pointer can be accessed on a byte-by-byte basis
by specifying the low or high byte in an instruction which
accesses the SFRs. See application note AN458 for more
details.
INC DPTRIncrements the data pointer by 1
MCV DPTR, #data 16
constant
MOV A, @ A+DPTR
MOVX A, @ DPTR
MOVX @ DPTR, A
JMP @ A + DPTR
EXTERNAL
MEMORY
DATA
MHI007
Loads the DPTR with a 16-bit
Move code byte relative to
DPTR to ACC
Move external RAM (16-bit
address) to ACC
Move ACC to external RAM
(16-bit address)
Jump indirect relative to
DPTR
Preliminary Specification
P8xC591