MC908AS60ACFU Datasheet, PDF (219/414 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

I/O Signals
To protect status bits during the break state, write a logic 0 to the BCFE bit. With BCFE at logic 0 (its
default state), software can read and write I/O registers during the break state without affecting status bits.
Some status bits have a two-step read/write clearing procedure. If software does the first step on such a
bit before the break, the bit cannot change during the break state as long as BCFE is at logic 0. After the
break, doing the second step clears the status bit.
Since the SPTE bit cannot be cleared during a break with the BCFE bit cleared, a write to the data register
in break mode will not initiate a transmission nor will this data be transferred into the shift register.
Therefore, a write to the SPDR in break mode with the BCFE bit cleared has no effect.
19.12 I/O Signals
The SPI module has four I/O pins and shares three of them with a parallel I/O port.
• MISO — Data received
• MOSI — Data transmitted
• SPSCK — Serial clock
• SS — Slave select
• V_SS — 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 V_DD.
19.12.1 MISO (Master In/Slave Out)
MISO is one of the two SPI module pins that transmit 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 0 and its SS pin is low. To support a multiple-slave system,
a high 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.
19.12.2 MOSI (Master Out/Slave In)
MOSI is one of the two SPI module pins that transmit 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.
19.12.3 SPSCK (Serial Clock)
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.
MC68HC908AZ60A • MC68HC908AS60A • MC68HC908AS60E Data Sheet, Rev. 6
Freescale Semiconductor
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