C8051F50x-F51x
Port
P0
P1
P2
P3
P4
P3.1-P3.7, P4.0 only
available on the 48-pin
and 40-pin packages
P4.1-P4.7 only
available on the 48-
pin packages
Special
Function
Signa ls
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
PIN I/O
UART_TX
UART_RX
CAN_TX
CAN_RX
SCK
MISO
MOSI
NSS
*NSS Is only pinned out in 4-wire SPI Mode
SDA
SCL
CP0
CP0A
CP1
CP1A
SYSCLK
CEX0
CEX1
CEX2
CEX3
CEX4
CEX5
ECI
T0
T1
LIN_TX
LIN_RX
0
1
1
0
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
P0SKIP[0:7]
P1SKIP[0:7]
P2SKIP[0:7]
P3SKIP[0:7]
Figure 20.4. Crossbar Priority Decoder in Example Configuration
20.4. Port I/O Initialization
Port I/O initialization consists of the following steps:
1. Select the input mode (analog or digital) for all Port pins, using the Port Input Mode register (PnMDIN).
2. Select the output mode (open-drain or push-pull) for all Port pins, using the Port Output Mode register
(PnMDOUT).
3. Select any pins to be skipped by the I/O Crossbar using the Port Skip registers (PnSKIP).
4. Assign Port pins to desired peripherals.
5. Enable the Crossbar (XBARE = 1).
All Port pins must be configured as either analog or digital inputs. Port 4 on the C8051F500/1/4/5 and
C8051F508/9-F510/1 is a digital-only Port. Any pins to be used as Comparator or ADC inputs should be
configured as an analog inputs. When a pin is configured as an analog input, its weak pullup, digital driver,
and digital receiver are disabled. This process saves power and reduces noise on the analog input. Pins
configured as digital inputs may still be used by analog peripherals; however this practice is not recom-
mended.
Additionally, all analog input pins should be configured to be skipped by the Crossbar (accomplished by
setting the associated bits in PnSKIP). Port input mode is set in the PnMDIN register, where a 1 indicates a
182
Rev. 1.1
SILICON [ SILICON ]
