Specifications

Serial Communications (V40)
If the counter/timers are driven with the external TCLK pin through
connector J3, instead of with the V40 clock, use the formula below
for calculating the value to be loaded into counter/timer 1. Note that
the frequency of the external clock signal is not dependent on the PS
bit of the TCKS register.
Count = External Clock / (Baud Rate x Baud Factor)
Interrupt and Polled
Communication
Serial data can be transferred and received either by polling status bits
or with interrupts. In a polled mode, the application program monitors
the SST register Transmit Buffer Ready and Receive Buffer Ready
signals to determine when to transfer a character to the SCU or when
a character is available.
The SCU is capable of generating interrupts for applications that
cannot afford time spent polling for status. A transmit interrupt is
generated when the transmitter is enabled, the transmit interrupt is not
masked, and the Serial Transmit Buffer is empty. A receive interrupt
occurs when the receiver is enabled, the receive interrupt is not
masked, and a character is received by the Serial Receive Buffer.
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