
I/O Signals
MC68HC08LK60 MC68HC908LK60 Advance Information Data Sheet, Rev. 1.1
Freescale Semiconductor
161
13.12 I/O Signals
The SPI module has five dedicated I/O pins.
MISO — Data received
MOSI — Data transmitted
SPSCK — Serial clock
SS — Slave select
EVSS — Clock ground
The SPI has limited inter-integrated circuit (I2C) capability (requiring software support) as a master in a
single-master environment. To communicate with I2C peripherals, MOSI becomes an open-drain output
when the SPWOM bit in the SPI control register is set. In I2C communication, the MOSI and MISO pins
are connected to a bidirectional pin from the I2C peripheral and through a pullup resistor to VDD.
13.12.1 Master In/Slave Out (MISO)
MISO is one of the two SPI module pins that transmits serial data. In full- duplex operation, the MISO pin
of the master SPI module is connected to the MISO pin of the slave SPI module. The master SPI
simultaneously receives data on its MISO pin and transmits data from its MOSI pin.
Slave output data on the MISO pin is enabled only when the SPI is configured as a slave. The SPI is
configured as a slave when its SPMSTR bit is logic 0 and its SS pin is at logic 0. To support a
multiple-slave system, a logic 1 on the SS pin puts the MISO pin in a high-impedance state.
When enabled, the SPI controls data direction of the MISO pin regardless of the state of the data direction
register of the shared I/O port.
NOTE
The MISO pin on this device is not shared with an I/O port.
13.12.2 Master Out/Slave In (MOSI)
MOSI is one of the two SPI module pins that transmits serial data. In full duplex operation, the MOSI pin
of the master SPI module is connected to the MOSI pin of the slave SPI module. The master SPI
simultaneously transmits data from its MOSI pin and receives data on its MISO pin.
When enabled, the SPI controls data direction of the MOSI pin regardless of the state of the data direction
register of the shared I/O port.
NOTE
The MOSI pin on this device is not shared with an I/O port.
13.12.3 Serial Clock (SPSCK)
The serial clock synchronizes data transmission between master and slave devices. In a master MCU,
the SPSCK pin is the clock output. In a slave MCU, the SPSCK pin is the clock input. In full-duplex
operation, the master and slave MCUs exchange a byte of data in eight serial clock cycles.
When enabled, the SPI controls data direction of the SPSCK pin regardless of the state of the data
direction register of the shared I/O port.
NOTE
The SPSCK pin on this device is not shared with an I/O port.