DS87C550 High-Speed Microcontroller User’s Guide Supplement
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Port 0 (P0)
7
6
5
4
3
2
1
0
SFR 80h
P0.7
P0.6
P0.5
P0.4
P0.3
P0.2
P0.1
P0.0
RW-1
RW-1
RW-1
RW-1
RW-1
RW-1
RW-1
RW-1
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
P0.7-0
Port 0.
This port functions as a multiplexed address/data bus during external
memory access, and as a general purpose I/O port on devices with internal
program memory. During external memory cycles, this port drives the LSB of the
address when ALE is high, and data when ALE is low. When used as a general
purpose I/O, this port is open-drain and requires pull-ups. Writing a 1 to any pin
of this port places it in a high impedance mode, which is required if the pin is to
be used as an input. Pull-ups are not required when used as a memory interface.
Stack Pointer (SP)
7
6
5
4
3
2
1
0
SFR 81h
SP.7
SP.6
SP.5
SP.4
SP.3
SP.2
SP.1
SP.0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-1
RW-1
RW-1
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
SP.7-0
Bits 7-0
Stack Pointer.
This stack pointer identifies the location where the stack will
begin. The stack pointer is incremented before every PUSH operation. This
register defaults to 07h after reset.
Data Pointer Low 0 (DPL)
7
6
5
4
3
2
1
0
SFR 82h
DPL.7
DPL.6
DPL.5
DPL.4
DPL.3
DPL.2
DPL.1
DPL.0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
DPL.7-0
Bits 7-0
Data Pointer Low 0.
This register is the low byte of the standard 80C32 16-bit
data pointer. DPL and DPH are used to point to non-scratchpad data RAM.
Data Pointer High 0 (DPH)
7
6
5
4
3
2
1
0
SFR 83h
DPH.7
DPH.6
DPH.5
DPH.4
DPH.3
DPH.2
DPH.1
DPH.0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
DPH.7-0
Bits 7-0
Data Pointer High 0.
This register is the high byte of the standard 80C32 16-bit
data pointer. DPL and DPH are used to point to non-scratchpad data RAM.
