MC68HC08AS32A Datasheet, PDF (184/296 Pages) Motorola, Inc – Microcontrollers

Freescale Semiconductor, Inc.
Serial Communications Interface (SCI)
With the misaligned character shown in Figure 13-9, 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
-1---5---4-----^–----1----6---0-- ^{× 100 = 3.9·0%}
154
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 13-9, 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
1----7---0-----–_{-----1---7---6-- × 100 = 3.53%}
170
13.4.3.6 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 logic 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 logic 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.
Data Sheet
184
Serial Communications Interface (SCI)
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MC68HC08AS32A — Rev. 1
MOTOROLA