Programmable Digital I/O And Crossbar; Figure 1.11. Digital Crossbar Diagram - Silicon Laboratories C8051F12 Series Manual

C8051F120/1/2/3/4/5/6/7 C8051F130/1/2/3
1.5.

Programmable Digital I/O and Crossbar

The standard 8051 8-bit Ports (0, 1, 2, and 3) are available on the MCUs. The devices in the larger (100-
pin TQFP) packaging have 4 additional ports (4, 5, 6, and 7) for a total of 64 general-purpose port I/O. The
Port I/O behave like the standard 8051 with a few enhancements.
Each Port I/O pin can be configured as either a push-pull or open-drain output. Also, the "weak pullups"
which are normally fixed on an 8051 can be globally disabled, providing additional power saving capabili-
ties for low-power applications.
Perhaps the most unique enhancement is the Digital Crossbar. This is a large digital switching network that
allows mapping of internal digital system resources to Port I/O pins on P0, P1, P2, and P3. (See
Figure 1.11) Unlike microcontrollers with standard multiplexed digital I/O, all combinations of functions are
supported.
The on-chip counter/timers, serial buses, HW interrupts, ADC Start of Conversion inputs, comparator out-
puts, and other digital signals in the controller can be configured to appear on the Port I/O pins specified in
the Crossbar Control registers. This allows the user to select the exact mix of general purpose Port I/O and
digital resources needed for the particular application.
2
Highest
UART0
Priority
4
SPI
2
SMBus
2
UART1
7
PCA
2
Comptr.
Outputs
T0, T1,
T2, T2EX,
8
T4,T4EX
/INT0,
/INT1
Lowest /SYSCLK divided by 1,2,4, or 8
Priority
CNVSTR0/2
8
P0
(P0.0-P0.7)
8
P1
(P1.0-P1.7)
Port
8
Latches
P2
(P2.0-P2.7)
8
P3
(P3.0-P3.7)
32
XBR0, XBR1,
XBR2, P1MDIN
Registers
Priority
Decoder
Digital
Crossbar
2
To External
Memory
Interface
(EMIF)

Figure 1.11. Digital Crossbar Diagram

Rev. 1.4
P0MDOUT, P1MDOUT,
P2MDOUT, P3MDOUT
Registers
P0
8
I/O
Cells
P1
8
I/O
Cells
P2
8
I/O
Cells
P3
8
I/O
Cells
To ADC2 Input
('F12x Only)
External
Pins
P0.0
Highest
Priority
P0.7
P1.0
P1.7
P2.0
P2.7
P3.0
Lowest
Priority
P3.7