C8051F360/1/2/3/4/5/6/7/8/9
17.1. Priority Crossbar Decoder
The Priority Crossbar Decoder (Figure 17.3) assigns a priority to each I/O function, starting at the top with
UART0. When a digital resource is selected, the least-significant unassigned Port pin is assigned to that
resource (excluding UART0, which will be assigned to specific port pins (P0.1 and P0.2 in the
C8051F360/3 devices, P0.4 and P0.5 in the C8051F361/2/4/5/6/7/8/9 devices). If a Port pin is assigned,
the Crossbar skips that pin when assigning the next selected resource. Additionally, the Crossbar will skip
Port pins whose associated bits in the PnSKIP registers are set. The PnSKIP registers allow software to
skip Port pins that are to be used for analog input, dedicated functions, or GPIO.
Important Note on Crossbar Configuration: If a Port pin is claimed by a peripheral without use of the
Crossbar, its corresponding PnSKIP bit should be set. This applies to the port pins associated with the
external oscillator, V , external CNVSTR signal, IDA0, and any selected ADC or comparator inputs. The
REF
Crossbar skips selected pins as if they were already assigned, and moves to the next unassigned pin.
Figure 17.3 shows the Crossbar Decoder priority with no Port pins skipped (P0SKIP, P1SKIP, P2SKIP,
P3SKIP = 0x00); Figure 17.4 shows the Crossbar Decoder priority with the P1.0 and P1.1 pins skipped
(P1SKIP = 0x03).
P0
P1
P2
P3
P3.5-P3.7
available
on 48-pin
only
SF Signals
(32- and 28-
pin)
P3.1-P3.4
available on
32/48-pin only
SF Signals
(48-pin)
PIN I/O
TX0
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
(32-pin and 28-pin packages)
(48-pin package)
RX0
TX0
RX0
SCK
MISO
MOSI
NSS*
SDA
SCL
(*4-Wire SPI Only)
CP0
CP0A
CP1
CP1A
/SYSCLK
CEX0
CEX1
CEX2
CEX3
CEX4
CEX5
ECI
T0
T1
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
0
0
0
0
0
0
P0SKIP[0:7]
P1SKIP[0:7]
P2SKIP[0:7]
P3SKIP[0:7]
Figure 17.3. Crossbar Priority Decoder with No Pins Skipped
Rev. 1.0
185
SILICON [ SILICON ]
