MSC8144E Reference Manual, Rev. 3
20-20
Freescale
Semiconductor
UART
20.2.6.2 Fast Data Tolerance
Figure 20-18 shows how much a fast received frame can be misaligned without causing a noise
error or a framing error. The fast stop bit ends at RT10 instead of RT16, but it is still sampled at
RT8, RT9, and RT10.
For an 8-bit data character, data sampling of the stop bit takes the receiver 9 bit times
×
16 RT
10 RT cycles = 154 RT cycles. With the misaligned character shown in Figure 20-18,
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:
((154 – 160) / 154)
×
100 = 3.90%
For a 9-bit data character, data sampling of the stop bit takes the receiver 10 bit
×
16 RT
10 RT cycles = 170 RT cycles. With the misaligned character, the receiver counts 170 RT cycles
at the point when the count of the transmitting device is 11 bit
×
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:
((170 – 176) / 170)
×
100 = 3.53%
20.2.7 Receiver Wake-Up
The receiver can be put into a standby state, so that the UART (SCI) can ignore transmissions
intended only for other receivers in multiple-receiver systems. This is sometimes called putting
the receiver to sleep. Setting the receiver wake-up (RWU) bit in the SCICR puts the receiver into
a standby state during which receiver interrupts are disabled. The SCI still loads the receive data
into the SCIDR, but it does not set the SCISR[RDRF] flag or any other flag. The transmitting
device can address messages to selected receivers by including addressing information in the
initial frame or frames of each message. Once the receiver is asleep, there must be a wake-up
procedure to allow it to respond to messages addressed to it. The SCICR[WAKE] bit determines
how the SCI is brought out of the standby state to process an incoming message. This wake bit
enables either idle line wake-up or address mark wake-up.
Figure 20-18. Fast Data
Idle or Next Frame
Stop
RT
1
RT
2
RT
3
RT
4
RT
5
RT
6
RT
7
RT
8
RT
9
RT
1
0
RT
1
1
RT
1
2
RT
1
3
RT
1
4
RT
1
5
RT
1
6
Data
Samples
Receiver
RT Clock
Summary of Contents for MSC8144E
Page 1: ...MSC8144E Reference Manual Quad Core Media Signal Processor MSC8144ERM Rev 3 July 2009 ...
Page 48: ...MSC8144E Reference Manual Rev 3 xlviii Freescale Semiconductor ...
Page 86: ...MSC8144E Reference Manual Rev 3 1 38 Freescale Semiconductor Overview ...
Page 168: ...MSC8144E Reference Manual Rev 3 3 60 Freescale Semiconductor External Signals ...
Page 242: ...MSC8144E Reference Manual Rev 3 5 26 Freescale Semiconductor Reset ...
Page 314: ...MSC8144E Reference Manual Rev 3 8 24 Freescale Semiconductor General Configuration Registers ...
Page 414: ...MSC8144E Reference Manual Rev 3 10 14 Freescale Semiconductor MSC8144E SC3400 DSP Subsystem ...
Page 452: ...MSC8144E Reference Manual Rev 3 11 38 Freescale Semiconductor Internal Memory Subsystem ...
Page 520: ...MSC8144E Reference Manual Rev 3 12 68 Freescale Semiconductor DDR SDRAM Memory Controller ...
Page 1070: ...MSC8144E Reference Manual Rev 3 21 28 Freescale Semiconductor Timers ...