c8051t602 Silicon Laboratories, c8051t602 Datasheet - Page 98

• Manufacturer Part Number: c8051t602
• Description: Mixed Signal Otp Eprom Mcu Family
• Manufacturer: Silicon Laboratories

C8051T600/1/2/3/4/5
13.1. Priority Crossbar Decoder
The Priority Crossbar Decoder (Figure 13.3) 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 is always at pins 4 and 5). 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 XBR0 register are set. The XBR0 register allows software to skip Port pins that are to
be used for analog input or GPIO.
Important Note on Crossbar Configuration: If a Port pin is claimed by a peripheral without use of the
Crossbar, its corresponding XBR0 bit should be set. This applies to P0.0 if V
external oscillator circuit is enabled, P0.6 if the ADC is configured to use the external conversion start sig-
nal (CNVSTR), and any selected ADC or Comparator inputs. The Crossbar skips selected pins as if they
were already assigned, and moves to the next unassigned pin. Figure 13.3 shows the Crossbar Decoder
priority with no Port pins skipped (XBR0 = 0x00); Figure 13.4 shows the Crossbar Decoder priority with
pins 6 and 2 skipped (XBR0 = 0x44).
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Figure 13.3. Crossbar Priority Decoder with XBR0 = 0x00
SF Signals
PIN I/O
TX0
RX0
SDA
SCL
CP0
CP0A
SYSCLK
CEX0
CEX1
CEX2
ECI
T0
T1
SF Signals
VREF
Port pin potentially available to peripheral
Special Function Signals are not assigned by the crossbar.
When these signals are enabled, the CrossBar must be
manually configured to skip their corresponding port pins.
0
0
1
0
2
0
EXTCLK
XBR0[0:7]
3
0
Rev. 0.5
P0
4
0
5
0
CNVSTR
6
0
7
0
REF
is enabled, P0.3 if the