C8051F360/1/2/3/4/5/6/7/8/9
17.3. General Purpose Port I/O
Port pins that remain unassigned by the Crossbar and are not used by analog peripherals can be used for
general purpose I/O. Ports P0-P3 are accessed through corresponding special function registers (SFRs)
that are both byte-addressable and bit-addressable. Port 4 (C8051F360/3 only) uses an SFR which is
byte-addressable. When writing to a Port, the value written to the SFR is latched to maintain the output
data value at each pin. When reading, the logic levels of the Port's input pins are returned regardless of the
XBRn settings (i.e., even when the pin is assigned to another signal by the Crossbar, the Port register can
always read its corresponding Port I/O pin). The exception to this is the execution of the read-modify-write
instructions that target a Port Latch register as the destination. The read-modify-write instructions when
operating on a Port SFR are the following: ANL, ORL, XRL, JBC, CPL, INC, DEC, DJNZ and MOV, CLR or
SETB, when the destination is an individual bit in a Port SFR. For these instructions, the value of the latch
register (not the pin) is read, modified, and written back to the SFR.
In addition to performing general purpose I/O, P0, P1, and P2 can generate a port match event if the logic
levels of the Port’s input pins match a software controlled value. A port match event is generated if
(P0 & P0MASK) does not equal (P0MATCH & P0MASK), if (P1 & P1MASK) does not equal
(P1MATCH & P1MASK), or if (P2 & P2MASK) does not equal (P2MATCH & P2MASK). This allows Soft-
ware to be notified if a certain change or pattern occurs on P0, P1, or P2 input pins regardless of the XBRn
settings. A port match event can cause an interrupt if EMAT (EIE2.1) is set to '1' or cause the internal oscil-
lator to awaken from SUSPEND mode. See Section “16.1.1. Internal Oscillator Suspend Mode” on
page 170 for more information.
SFR Definition 17.3. P0: Port0
SFR Page:
SFR Address: 0x80
all pages
(bit addressable)
R/W
R/W
R/W
P0.5
Bit5
R/W
P0.4
Bit4
R/W
P0.3
Bit3
R/W
P0.2
Bit2
R/W
P0.1
Bit1
R/W
P0.0
Bit0
Reset Value
P0.7
Bit7
P0.6
Bit6
11111111
Bits 7–0: P0.[7:0]
Write - Output appears on I/O pins per Crossbar Registers.
0: Logic Low Output.
1: Logic High Output (high impedance if corresponding P0MDOUT.n bit = 0).
Read - Always reads ‘0’ if selected as analog input in register P0MDIN. Directly reads Port
pin when configured as digital input.
0: P0.n pin is logic low.
1: P0.n pin is logic high.
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Rev. 1.0
SILICON [ SILICON ]
