Z8 Encore!® Motor Control Flash MCUs
Product Specification
152
Serial Clock
The Serial Clock (SCK) synchronizes data movement both in and out of the device
through its MOSI and MISO pins. In MASTER mode, the SPI’s Baud Rate Generator cre-
ates the serial clock. The master drives the serial clock through its own serial clock (SCK)
pin to the slave’s SCK pin. When the SPI is configured as a slave, the SCK pin is an input
and the clock signal from the master synchronizes the data transfer between the master and
slave devices. These slave devices ignore the SCK signal unless the SS pin is asserted.
When configured as a slave, the SPI block requires a minimum SCK period of greater than
or equal to 8 times the system (XIN) clock period.
The master and slave are each capable of exchanging a character of data during a sequence
of NUMBITSclock cycles (refer to the NUMBITSfield in the SPIMODE Register). In both
master and slave SPI devices, data is shifted on one edge of the SCK and is sampled on the
opposite edge, where data is stable. Edge polarity is determined by the SPI phase and
polarity control.
Slave Select
The active Low Slave Select (SS) input signal selects a slave SPI device. SS must be Low
prior to all data communication to and from the slave device. SS must remain Low for the
full duration of each character transferred. The SS signal may stay Low during the transfer
of multiple characters, or may deassert between each character.
When the SPI is configured as the only master in an SPI system, the SS pin can be set as
either an input or an output. For communication between the Z8 Encore!® 8K Series
device’s SPI master and external slave devices, the SS signal, as an output, can assert the
SS input pin on one of the slave devices. Other GPIO output pins can also be employed to
select external SPI slave devices.
When the SPI is configured as one master in a multimaster SPI system, the SS pin should
be set as an input. The SS input signal on the master must be High. If the SS signal goes
Low (indicating that another master is driving the SPI bus), a collision error flag is set in
the SPI Status Register.
SPI Clock Phase and Polarity Control
The SPI supports four combinations of serial clock phase and polarity using two bits in the
SPI Control Register. The clock polarity bit, CLKPOL, selects an active High or active
Low clock and has no effect on the transfer format. Table 83 lists the SPI Clock Phase and
Polarity Operation parameters. The clock phase bit, PHASE, selects one of two fundamen-
tally different transfer formats. For proper data transmission, clock phase and polarity
must be identical for the SPI master and the SPI slave. The master always places data on
the MOSI line a half-cycle before the receive clock edge (SCK signal) for the slave to
latch the data.
Serial Peripheral Interface
P R E L I M I N A R Y
PS024604-1005
ZILOG [ ZILOG, INC. ]
