Datasheet

Functional Description
MC68HC908AP Family Data Sheet, Rev. 4
Freescale Semiconductor 165
The maximum percent difference between the receiver count and the transmitter count of a slow 9-bit
character with no errors is
Fast Data Tolerance
Figure 11-8 shows how much a fast received character can be misaligned without causing a noise error
or a framing error. The fast stop bit ends at RT10 instead of RT16 but is still there for the stop bit data
samples at RT8, RT9, and RT10.
Figure 11-8. Fast Data
For an 8-bit character, data sampling of the stop bit takes the receiver
9 bit times × 16 RT cycles + 10 RT cycles = 154 RT cycles.
With the misaligned character shown in Figure 11-8, 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 11-8, 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
11.4.3.6 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.
170 163–
170
--------------------------
100× 4.12%=
IDLE OR NEXT CHARACTERSTOP
RT1 RT2 RT3 RT4 RT5 RT6 RT7 RT8 RT9
RT10 RT11 RT12 RT13 RT14 RT15 RT16
DATA
SAMPLES
RECEIVER
RT CLOCK
154 160–
154
--------------------------
100× 3.90%
˙
=
170 176–
170
--------------------------
100× 3.53%=