Serial Interface
MPC885 PowerQUICC Family Reference Manual, Rev. 2
Freescale Semiconductor
20-37
Figure 20-29
shows a baud rate generator.
Figure 20-29. Baud Rate Generator (BRG) Block Diagram
The BRG clock source can be BRGCLK, CLK2, or CLK6 (selected in BRGCn[EXTC]). The BRGCLK
is generated in the MPC885 clock synthesizer specifically for the BRGs, the SPI, and the I
2
C internal baud
rate generator. Alternatively, the CLK2 and CLK6 pins can be configured as clock sources. These external
source options allow flexible baud rate frequency generation, independent of the system frequency.
Additionally, CLK2 and CLK6 allow a single external frequency to be the source for multiple BRGs. Note
that the CLK2 and CLK6 signals are not synchronized internally before being used by the BRG.
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 fly;
however, two changes should not occur within 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 odd, 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.
20.4.1
Baud Rate Generator Configuration Registers (BRGC
n
)
Each baud rate generator configuration register (BRGC), shown in
Figure 20-30
, 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. Configuration 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 fly; however, two changes should not occur within a time equal to two source clock periods.
CLK2 Pin
Clock
Source
MUX
Divide by
1 or 16
Prescaler
12-Bit Counter
1 – 4,096
DIV 16
CD[0–11]
BRGOn Clock
BRGCLK
EXTC
ATB
Autobaud
Control
RXD
n
To Pin and/or
Bank of Clocks
BRG
n
CLK6 Pin
Содержание PowerQUICC MPC870
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Страница 118: ...MPC885 Overview MPC885 PowerQUICC Family Reference Manual Rev 2 1 20 Freescale Semiconductor ...
Страница 158: ...The MPC8xx Core MPC885 PowerQUICC Family Reference Manual Rev 2 3 18 Freescale Semiconductor ...
Страница 192: ...MPC885 Instruction Set MPC885 PowerQUICC Family Reference Manual Rev 2 5 22 Freescale Semiconductor ...
Страница 242: ...Instruction and Data Caches MPC885 PowerQUICC Family Reference Manual Rev 2 7 30 Freescale Semiconductor ...
Страница 288: ...MPC885 PowerQUICC Family Reference Manual Rev 2 III 4 Freescale Semiconductor ...
Страница 416: ...External Bus Interface MPC885 PowerQUICC Family Reference Manual Rev 2 13 42 Freescale Semiconductor ...
Страница 440: ...Clocks and Power Control MPC885 PowerQUICC Family Reference Manual Rev 2 14 24 Freescale Semiconductor ...
Страница 554: ...MPC885 PowerQUICC Family Reference Manual Rev 2 V 6 Freescale Semiconductor ...
Страница 606: ...SDMA Channels and IDMA Emulation MPC885 PowerQUICC Family Reference Manual Rev 2 19 20 Freescale Semiconductor ...
Страница 738: ...SCC Asynchronous HDLC Mode and IrDA MPC885 PowerQUICC Family Reference Manual Rev 2 25 16 Freescale Semiconductor ...
Страница 780: ...SCC Ethernet Mode MPC885 PowerQUICC Family Reference Manual Rev 2 27 24 Freescale Semiconductor ...
Страница 794: ...SCC Transparent Mode MPC885 PowerQUICC Family Reference Manual Rev 2 28 14 Freescale Semiconductor ...
Страница 848: ...Serial Peripheral Interface SPI MPC885 PowerQUICC Family Reference Manual Rev 2 30 18 Freescale Semiconductor ...
Страница 882: ...Universal Serial Bus USB MPC885 PowerQUICC Family Reference Manual Rev 2 31 34 Freescale Semiconductor ...
Страница 944: ...Parallel I O Ports MPC885 PowerQUICC Family Reference Manual Rev 2 34 26 Freescale Semiconductor ...
Страница 956: ...CPM Interrupt Controller MPC885 PowerQUICC Family Reference Manual Rev 2 35 12 Freescale Semiconductor ...
Страница 1004: ...Buffer Descriptors and Connection Tables MPC885 PowerQUICC Family Reference Manual Rev 2 37 30 Freescale Semiconductor ...
Страница 1022: ...ATM Parameter RAM MPC885 PowerQUICC Family Reference Manual Rev 2 38 18 Freescale Semiconductor ...
Страница 1068: ...ATM Pace Control MPC885 PowerQUICC Family Reference Manual Rev 2 40 22 Freescale Semiconductor ...
Страница 1090: ...UTOPIA Interface MPC885 PowerQUICC Family Reference Manual Rev 2 43 8 Freescale Semiconductor ...
Страница 1120: ...AAL2 Implementation MPC885 PowerQUICC Family Reference Manual Rev 2 44 30 Freescale Semiconductor ...
Страница 1162: ...Fast Ethernet Controller FEC MPC885 PowerQUICC Family Reference Manual Rev 2 45 40 Freescale Semiconductor ...
Страница 1172: ...SEC Lite Overview MPC885 PowerQUICC Family Reference Manual Rev 2 46 8 Freescale Semiconductor ...
Страница 1176: ...SEC Lite Address Map MPC885 PowerQUICC Family Reference Manual Rev 2 47 4 Freescale Semiconductor ...
Страница 1214: ...SEC Lite Execution Units MPC885 PowerQUICC Family Reference Manual Rev 2 48 38 Freescale Semiconductor ...
Страница 1312: ...Byte Ordering MPC885 PowerQUICC Family Reference Manual Rev 2 A 8 Freescale Semiconductor ...
Страница 1313: ...MPC885 PowerQUICC Family Reference Manual Rev 2 Freescale Semiconductor B 1 Appendix B Serial Communications Performance TBD ...
Страница 1314: ...Serial Communications Performance MPC885 PowerQUICC Family Reference Manual Rev 2 B 2 Freescale Semiconductor ...
Страница 1320: ...Register Quick Reference Guide MPC885 PowerQUICC Family Reference Manual Rev 2 C 6 Freescale Semiconductor ...
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Страница 1370: ...MPC880 MPC885 PowerQUICC Family Reference Manual Rev 2 E 4 Freescale Semiconductor ...
Страница 1384: ...Serial ATM Scrambling Reception and SI Programming MPC885 PowerQUICC Family Reference Manual Rev 2 H 6 Freescale Semiconductor ...
Страница 1386: ...Revision History MPC885 PowerQUICC Family Reference Manual Rev 2 I 2 Freescale Semiconductor ...