C8051F360/1/2/3/4/5/6/7/8/9
17. Port Input/Output
Digital and analog resources are available through up to 39 I/O pins. On the largest devices
(C8051F360/3), port pins are organized as four byte-wide Ports and one 7-bit-wide Port. On the other
devices (C8051F361/2/4/5/6/7/8/9), port pins are three byte-wide Ports and one partial port. Each of the
Port pins can be defined as general-purpose I/O (GPIO) or analog input/output; Port pins P0.0–P3.7 can
be assigned to one of the internal digital resources as shown in Figure 17.3. The designer has complete
control over which functions are assigned, limited only by the number of physical 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, regardless of the Crossbar settings.
The Crossbar assigns the selected internal digital resources to the I/O pins based on the peripheral priority
order of the Priority Decoder (Figure 17.3 and Figure 17.4). The registers XBR0 and XBR1, defined in SFR
Definition 17.1 and SFR Definition 17.2, are used to select internal digital functions.
All Port I/Os are 5 V tolerant (refer to Figure 17.2 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 = 0,1,2,3,4). Com-
plete Electrical Specifications for Port I/O are given in Table 17.1 on page 201.
P0MASK, P0MATCH
P1MASK, P1MATCH,
P2MASK, P2MATCH
Registers
XBR0, XBR1,
PnSKIP Registers
PnMDOUT,
PnMDIN Registers
Priority
Decoder
2
P0.0
P0.7
P0
I/O
Cells
UART
SPI
Highest
Priority
8
4
2
P1.0
P1.7
P1
I/O
Cells
8
8
SMBus
Digital
Crossbar
CP0
CP1
Outputs
4
P2.0
P2.7
P3.0
P3.7
P2
I/O
Cell
SYSCLK
PCA
7
2
3.1–3.4 available on
C8051F360/1/3/4/6/8
P3
I/O
Cells
8
Lowest
Priority
T0, T1
8
3.5–3.7 available on
C8051F360/3
P0
P1
P2
P3
(P0.0-P0.7)
8
(P1.0-P1.7)
8
(P2.0-P2.7)
8
(P3.0-P3.7)
Figure 17.1. Port I/O Functional Block Diagram (Port 0 through Port 3)
Rev. 1.0
183
SILICON [ SILICON ]
