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Serial Communications Interface (SCI) Module
Data Sheet
MC68HC08GP32A MC68HC08GP16A
162
Serial Communications Interface (SCI) Module
MOTOROLA
With the misaligned character shown in Figure 14-9, the receiver counts 154 RT
cycles at the point when the count of the transmitting device is
10 bit times
× 16 RT cycles = 160 RT cycles.
The maximum percent difference between the receiver count and the transmitter
count of a fast 8-bit character with no errors is
For a 9-bit character, data sampling of the stop bit takes the receiver
10 bit times
× 16 RT cycles + 10 RT cycles = 170 RT cycles.
With the misaligned character shown in Figure 14-9, the receiver counts 170 RT
cycles at the point when the count of the transmitting device is
11 bit times
× 16 RT cycles = 176 RT cycles.
The maximum percent difference between the receiver count and the transmitter
count of a fast 9-bit character with no errors is
14.4.3.6 Receiver Wakeup
So that the MCU can ignore transmissions intended only for other receivers in
multiple-receiver systems, the receiver can be put into a standby state. Setting the
receiver wakeup bit, RWU, in SCC2 puts the receiver into a standby state during
which receiver interrupts are disabled.
Depending on the state of the WAKE bit in SCC1, either of two conditions on the
PTE1/RxD pin can bring the receiver out of the standby state:
Address mark — An address mark is a 1 in the most significant bit position
of a received character. When the WAKE bit is set, an address mark wakes
the receiver from the standby state by clearing the RWU bit. The address
mark also sets the SCI receiver full bit, SCRF. Software can then compare
the character containing the address mark to the user-defined address of
the receiver. If they are the same, the receiver remains awake and
processes the characters that follow. If they are not the same, software can
set the RWU bit and put the receiver back into the standby state.
Idle input line condition — When the WAKE bit is clear, an idle character on
the PTE1/RxD pin wakes the receiver from the standby state by clearing the
RWU bit. The idle character that wakes the receiver does not set the
receiver idle bit, IDLE, or the SCI receiver full bit, SCRF. The idle line type
bit, ILTY, determines whether the receiver begins counting 1s as idle
character bits after the start bit or after the stop bit.
NOTE:
With the WAKE bit clear, setting the RWU bit after the RxD pin has been idle may
cause the receiver to wake up immediately.
154
160
–
154
--------------------------
100
×
3.90%
=
170
176
–
170
--------------------------
100
×
3.53%
=