C8051F50x-F51x
20. Port Input/Output
Digital and analog resources are available through 40 (C8051F500/1/4/5), 33 (C8051F508/9-F510/1) or 25
(C8051F502/3/6/7) I/O pins. Port pins P0.0-P4.7 on the C8051F500/1/4/5, port pins P0.0-P4.0 on
theC8051F508/9-F510/1, and port pins P0.0-P3.0 on the C8051F502/3/6/7 can be defined as general-pur-
pose I/O (GPIO), assigned to one of the internal digital resources, or assigned to an analog function as
shown in Figure 20.3. Port pin P4.0 on the C8051F508/9-F510/1 can be used as GPIO and is shared with
the C2 Interface Data signal (C2D). Similarly, port pin P3.0 is shared with C2D on the C8051F502/3/6/7.
The designer has complete control over which functions are assigned, limited only by the number of phys-
ical I/O pins. This resource assignment flexibility is achieved through the use of a Priority Crossbar
Decoder. Note that the state of a Port I/O pin can always be read in the corresponding Port latch, regard-
less of the Crossbar settings.
The Crossbar assigns the selected internal digital resources to the I/O pins based on the Priority Decoder
(Figure 20.3 and Figure 20.4). The registers XBR0, XBR1, XBR2 are defined in SFR Definition 20.1 and
SFR Definition 20.2 and are used to select internal digital functions.
All Port I/Os are 5 V tolerant (refer to Figure 20.2 for the Port cell circuit). The Port I/O cells are configured
as either push-pull or open-drain in the Port Output Mode registers (PnMDOUT, where n = 0,1). Complete
Electrical Specifications for Port I/O are given in Table 5.3 on page 45.
XBR0, XBR1,
XBR2, PnSKIP
PnMDOUT,
PnDMIN Registers
External
Pins
Priority
Decoder
2
2
4
2
P0.0
Highest
Priority
P0
I/O
Cells
UART0
CAN0
8
8
8
8
8
Highest
Priority
P0.7
Digital
Crossbar
SPI0
P1.0
P1.7
P1
I/O
Cells
SMBus0
2
2
CP0
P2.0
P2.7
P2
I/O
Cells
CP1
/SYSCLK
7
4
PCA0
P3.0
P3.7
P3
I/O
Cells
T0, T1,
/INT0,
/INT1
Lowest
Priority
2
LIN0
P4.0
P4.7
P4
I/O
Cells
Lowest
Priority
8 x 5
P0
P1
P2
P3
P4
Port
Latches
(Px.0-Px.7)
8 x 5
PnMASK
PnMATCH
Registers
Figure 20.1. Port I/O Functional Block Diagram
Rev. 1.1
177
SILICON [ SILICON ]
