Z8F6421PM020SC Datasheet, PDF (151/299 Pages) Zilog, Inc. – High Performance 8-Bit Microcontrollers Z8 Encore-R 64K Series

Z8 Encore!^® 64K Series
Product Specification
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ister. The IRQE, PHASE, CLKPOL, WOR bits in the SPICTL register and the NUMBITS
field in the SPIMODE register must be set to be consistent with the other SPI devices. The
STR bit in the SPICTL register may be used if desired to force a “startup” interrupt. The
BIRQ bit in the SPICTL register and the SSV bit in the SPIMODE register are not used in
slave mode. The SPI baud rate generator is not used in slave mode so the SPIBRH and
SPIBRL registers need not be initialized.
If the slave has data to send to the master, the data must be written to the SPIDAT register
before the transaction starts (first edge of SCK when SS is asserted). If the SPIDAT regis-
ter is not written prior to the slave transaction, the MISO pin outputs whatever value is
currently in the SPIDAT register.
Due to the delay resulting from synchronization of the SPI input signals to the internal sys-
tem clock, the maximum SPICLK baud rate that can be supported in slave mode is the sys-
tem clock frequency (XIN) divided by 8. This rate is controlled by the SPI master.
Error Detection
The SPI contains error detection logic to support SPI communication protocols and recog-
nize when communication errors have occurred. The SPI Status register indicates when a
data transmission error has been detected.
Overrun (Write Collision)
An overrun error (write collision) indicates a write to the SPI Data register was attempted
while a data transfer is in progress (in either master or slave modes). An overrun sets the
OVR bit in the SPI Status register to 1. Writing a 1 to OVR clears this error flag. The data
register is not altered when a write occurs while data transfer is in progress.
Mode Fault (Multi-Master Collision)
A mode fault indicates when more than one Master is trying to communicate at the same
time (a multi-master collision). The mode fault is detected when the enabled Master’s SS
pin is asserted. A mode fault sets the COL bit in the SPI Status register to 1. Writing a 1 to
COL clears this error flag.
Slave Mode Abort
In slave mode of operation if the SS pin deasserts before all bits in a character have been
transferred, the transaction is aborted. When this condition occurs the ABT bit is set in the
SPISTAT register as well as the IRQ bit (indicating the transaction is complete). The next
time SS asserts, the MISO pin outputs SPIDAT[7], regardless of where the previous trans-
action left off. Writing a 1 to ABT clears this error flag.
SPI Interrupts
When SPI interrupts are enabled, the SPI generates an interrupt after character transmis-
sion/reception completes in both master and slave modes. A character can be defined to be
PS019915-1005
Serial Peripheral Interface