Z8F6421PM020SC Datasheet, PDF (152/299 Pages) Zilog, Inc. – High Performance 8-Bit Microcontrollers Z8 Encore-R 64K Series

Z8 Encore!^® 64K Series
Product Specification
132
1 through 8 bits by the NUMBITS field in the SPI Mode register. In slave mode it is not
necessary for SS to deassert between characters to generate the interrupt. The SPI in Slave
mode can also generate an interrupt if the SS signal deasserts prior to transfer of all the bits
in a character (see description of slave abort error above). Writing a 1 to the IRQ bit in the
SPI Status Register clears the pending SPI interrupt request. The IRQ bit must be cleared
to 0 by the Interrupt Service Routine to generate future interrupts. To start the transfer pro-
cess, an SPI interrupt may be forced by software writing a 1 to the STR bit in the SPICTL
register.
If the SPI is disabled, an SPI interrupt can be generated by a Baud Rate Generator time-
out. This timer function must be enabled by setting the BIRQ bit in the SPICTL register.
This Baud Rate Generator time-out does not set the IRQ bit in the SPISTAT register, just
the SPI interrupt bit in the interrupt controller.
SPI Baud Rate Generator
In SPI Master mode, the Baud Rate Generator creates a lower frequency serial clock
(SCK) for data transmission synchronization between the Master and the external Slave.
The input to the Baud Rate Generator is the system clock. The SPI Baud Rate High and
Low Byte registers combine to form a 16-bit reload value, BRG[15:0], for the SPI Baud
Rate Generator. The SPI baud rate is calculated using the following equation:
SPI Baud Rate (bits/s) = ^{S----y---s--t--e---m------2C-----}_×^{l-o---cB---k-R----F-G---r-[-e-1--q-5--u-:--0-e--n]----c--y-----(--H----z---)}
Minimum baud rate is obtained by setting BRG[15:0] to 0000H for a clock divisor value
of (2 X 65536 = 131072).
When the SPI is disabled, the Baud Rate Generator can function as a basic 16-bit timer
with interrupt on time-out. To configure the Baud Rate Generator as a timer with interrupt
on time-out, complete the following procedure:
1. Disable the SPI by clearing the SPIEN bit in the SPI Control register to 0.
2. Load the desired 16-bit count value into the SPI Baud Rate High and Low Byte
registers.
3. Enable the Baud Rate Generator timer function and associated interrupt by setting the
BIRQ bit in the SPI Control register to 1.
When configured as a general purpose timer, the interrupt interval is calculated using the
following equation:
Interrupt Interval (s) = System Clock Period (s) ×BRG[15:0] ]
PS019915-1005
Serial Peripheral Interface