MCCIRM Freescale Semiconductor / Motorola, MCCIRM Datasheet - Page 63

• Manufacturer Part Number: MCCIRM
• Description: MCCIRM Multi-Channel Communications Interface Reference Manual
• Manufacturer: Freescale Semiconductor / Motorola

5.7 SCI Transmitter
Multichannel Communication Interface — Rev. 1.0
MOTOROLA
The SCI transmitter consists of a transmit serial shifter and a parallel
transmit data register (TDR) located in the SCDR. The transmitter is
double buffered: One byte can be loaded into the TDR while another
character is being shifted out from the serial shifter to the TXD pin.
Transmitter logic adds a start bit (logic 0) and a stop bit (logic 1) to the
data characters presented by the CPU for transmission. The transmitter
can be configured to send characters with eight (M = 0) or nine (M = 1)
data bits. When the TDR is able to accept a new data character, the
TDRE status flag is set, and an interrupt can optionally be generated.
Another status flag (TC) and optional interrupt are produced when the
transmitter has finished sending everything in its queue. In addition to
data characters, the transmitter is capable of sending idle-line
characters and break characters, which are useful in multidrop SCI
networks. Two characters can normally be in the transmit queue, but
three characters can be queued when at least one of them is an idle-line
or break character.
Figure 5-1
Freescale Semiconductor, Inc.
Baud Rate
For More Information On This Product,
Nominal
500,000
38,400
32,768
19,200
9,600
4,800
2,400
1,200
600
300
110
64
is a block diagram of the SCI transmitter.
Go to: www.freescale.com
Table 5-4. Examples of SCI Baud Rates
SCI Submodule
524,288.00
Baud Rate
37,499.14
32,768.00
19,418.07
9,532.51
4,809.98
2,404.99
1,199.74
Actual
599.87
299.94
110.01
64.00
Percent
–2.48
–0.70
–0.02
–0.02
–0.02
Error
4.86
0.00
1.14
0.21
0.21
0.01
0.01
Reference Manual
SCI Submodule
SCI Transmitter
1,748
4,766
8,191
109
218
437
874
BR
14
16
27
55
1
63