C8051F54X_14 Datasheet, PDF (161/275 Pages) Silicon Laboratories – Mixed Signal ISP Flash MCU Family

C8051F54x
18.6. Special Function Registers for Accessing and Configuring Port I/O
All Port I/O are accessed through corresponding special function registers (SFRs) that are both byte
addressable and bit addressable. When writing to a Port, the value written to the SFR is latched to main-
tain 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.
Ports 0–3 have a corresponding PnSKIP register which allows its individual Port pins to be assigned to dig-
ital functions or skipped by the Crossbar. All Port pins used for analog functions, GPIO, or dedicated digital
functions such as the EMIF should have their PnSKIP bit set to 1.
The Port input mode of the I/O pins is defined using the Port Input Mode registers (PnMDIN). Each Port
cell can be configured for analog or digital I/O. This selection is required even for the digital resources
selected in the XBRn registers, and is not automatic.
The output driver characteristics of the I/O pins are defined using the Port Output Mode registers (PnMD-
OUT). Each Port Output driver can be configured as either open drain or push-pull. This selection is
required even for the digital resources selected in the XBRn registers, and is not automatic. The only
exception to this is the SMBus (SDA, SCL) pins, which are configured as open-drain regardless of the
PnMDOUT settings.
SFR Definition 18.12. P0: Port 0
Bit
7
6
5
4
3
2
1
0
Name
P0[7:0]
Type
R/W
Reset
1
1
1
1
1
1
1
1
SFR Address = 0x80; SFR Page = All Pages; Bit-Addressable
Bit Name
Description
Write
Read
7:0 P0[7:0] Port 0 Data.
0: Set output latch to logic 0: P0.n Port pin is logic
Sets the Port latch logic
LOW.
LOW.
value or reads the Port pin ^{1: Set output latch to logic 1: P0.n Port pin is logic}
logic state in Port cells con- ^HIGH.
HIGH.
figured for digital I/O.
Rev. 1.1
161