原创 CC1110的I/O

The CC1110Fx has 21 digital input/output pins that can be configured as general purpose digital I/O or as peripheral I/O signals connected to the ADC, Timers, I2S, or USART peripherals. The usage of the I/O ports is fully configurable from user software through a set of configuration registers.
The I/O ports have the following key features:
? 21 digital input/output pins
? General purpose I/O or peripheral I/O
? Pull-up or pull-down capability on inputs, except on P1_0 and P1_1.
? External interrupt capability
The external interrupt capability is available on all 21 I/O pins. Thus, external devices may generate interrupts if required. The externalinterrupt feature can also be used to wake upfrom all four power modes (PM{0 - 3}).

When used as general purpose I/O, the pins are organized as three 8-bit ports, port 0, 1, and 2, denoted P0, P1, and P2. P0 and P1 are complete 8-bit wide ports while P2 has only five usable bits (P2_0 to P2_4). All ports are both bit- and byte addressable through the SFRs P0, P1 and P2. Each port pin can individually be set to operate as a general purpose I/O or as a peripheral I/O.

To use a port as a general purpose I/O pin the pin must first be configured. The registers PxSEL are used to configure each pin in a port either as a general purpose I/O pin or as a peripheral I/O signal. All digital input/output pins are configured as general-purpose I/O pins by default. Note that when the I2S interface is enabled (I2SCFG0.ENAB=1), the I2S interface will control its corresponding pins even if these are selected to be general purpose I/O pins in the PxSEL register.
By default, all general-purpose I/O pins are configured as inputs. To change the direction of a port pin, at any time, the registers PxDIR are used to set each port pin to be either an input or an output. Thus by setting the appropriate bit within PxDIR to 1, the corresponding pin becomes an output. When reading the port registers P0, P1, and P2, the logic values on the input pins are returned regardless of the pin configuration.
This does not apply during the execution of read-modify-write instructions. The readmodify-write instructions are: ANL, ORL, XRL, JBC, CPL, INC, DEC, DJNZ, and MOV, CLR, or SETB. Operating on a port registers the following is true: When the destination is an individual bit in a port register P0, P1 or P2 the value of the register, not the value on the pin, is read, modified, and written back to the port register.
When used as an input, the general purpose I/O port pins can be configured to have a pull-up, pull-down, or tri-state mode of operation. By default, inputs are configured as inputs with pull-up. To de-select the pull-up/pull-down function on an input the appropriate bit within the PxINP must be set to 1. The I/O port pins P1_0 and P1_1 do not have pull-up/pull-down capability.
In PM1, PM2, and PM3 the I/O pins retain the I/O mode and output value (if applicable) that was set when PM{1 - 3} was entered.