MC908JB16DWE Datasheet, PDF (225/332 Pages) Freescale Semiconductor, Inc – Microcontrollers

Serial Communications Interface Module (SCI)
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 12-8, 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
12.5.3.6 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 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 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
MC68HC908JB16 — Rev. 1.1
Freescale Semiconductor
Serial Communications Interface Module (SCI)
Technical Data
225