21-40
MPC860 PowerQUICC UserÕs Manual
MOTOROLA
Part V. The Communications Processor Module
The BRG provides a divide-by-16 option (BRGCn[DIV16]) and a 12-bit prescaler
(BRGCn[CD]) to divide the source clock frequency. The combined source-clock divide
factor can be changed on-the-ßy; however, two changes should not occur within a time
equal to two source clock periods.
The prescaler output is sent internally to the bank of clocks and can also be output
externally on BRGOn through either the port A or port B parallel I/O. If the BRG divides
the clock by an even value, the transitions of BRGOn always occur on the falling edge of
the source clock. If the divide factor is an odd value, the transitions alternate between the
falling and rising edges of the source clock. Additionally, the output of the BRG can be sent
to the autobaud control block.
21.4.1 Baud Rate Generator ConÞguration Registers (BRGCn)
Each baud rate generator conÞguration register (BRGC), shown in Figure 21-30, is cleared
at reset. A reset disables the BRG and drives the BRGO output clock high. The BRGC can
be written at any time with no need to disable the SCCs or external devices that are
connected to BRGO. ConÞguration changes occur at the end of the next BRG clock cycle
(no spikes occur on the BRGO output clock). BRGC can be changed on-the-ßy; however,
two changes should not occur within a time equal to two source clock periods.
Table 21-13 describes the BRGCn Þelds.
Bit
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Field
Ñ
RST
EN
Reset
0
R/W
R/W
Addr
0x9F0 (BRGC1), 0x9F4 (BRGC2), 0x9F8 (BRGC3), 0x9FC (BRGC4)
Bit
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Field
EXTC
ATB
CD
DIV16
Reset
0
R/W
R/W
Addr
0x9F2 (BRGC1), 0x9F6 (BRGC2), 0x9FA (BRGC3), 0x9FE (BRGC4)
Figure 21-30. Baud Rate Generator Configuration Registers (BRGCn)
Table 21-13. BRGCn Field Descriptions
Bits
Name
Description
0Ð13
Ñ
Reserved, should be cleared.
14
RST
Reset BRG. Performs a software reset of the BRG identical to that of an external reset. A reset
disables the BRG and drives BRGO high. This is externally visible only if BRGO is connected to the
corresponding parallel I/O pin.
0 Enable the BRG.
1 Reset the BRG (software reset).
Summary of Contents for MPC860 PowerQUICC
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Page 78: ...I iv MPC860 PowerQUICC UserÕs Manual MOTOROLA Part I Overview ...
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Page 226: ...8 32 MPC860 PowerQUICC UserÕs Manual MOTOROLA Part II PowerPC Microprocessor Module ...
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Page 274: ...III iv MPC860 PowerQUICC UserÕs Manual MOTOROLA Part III Configuration ...
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Page 325: ...MOTOROLA Part IV Hardware Interface IV v Part IV Hardware Interface ...
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