Serial Communications Controllers
MPC885 PowerQUICC Family Reference Manual, Rev. 2
Freescale Semiconductor
21-23
The DPLL can also be used to invert the data stream of a transfer. This feature is available in all encodings,
including standard NRZ format. Also, when the transmitter is idling, the DPLL can either force TXD high
or continue encoding the data supplied to it.
The DPLL is used for UART encoding/decoding, which gives the option of selecting the divide ratio in
the UART decoding process (8
×
, 16
×
, or 32
×
). Typically, 16
×
is used.
The maximum data rate supported with the DPLL is 3.125 MHz, assuming a 25-MHz system clock and
the 8
×
ratio (25 MHz/8 = 3.125 MHz). Thus, the frequency applied to CLKx or generated by an internal
baud rate generator may be up to 25 MHz on a 25-MHz MPC885, if the DPLL 8
×
, 16
×
, or 32
×
option is
used.
Note the 1:2 system clock/serial clock ratio does not apply when the DPLL is used to recover the clock in
the 8
×
, 16
×
, or 32
×
modes. Synchronization occurs internally after the DPLL generates the Rx clock.
Therefore, even the fastest DPLL clock generation (the 8
×
option) easily meets the required 1:2 ratio
clocking limit.
21.4.5.1
Encoding Data with a DPLL
Each SCC contains a DPLL unit that can be programmed to encode and decode the SCC data as NRZ,
NRZI Mark, NRZI Space, FM0, FM1, Manchester, and Differential Manchester.
Figure 21-15
shows the
different encoding methods.
Table 21-8. Preamble Requirements
Decoding Method
Preamble Pattern
Minimum Preamble Length Required
NRZI Mark
All zeros
8-bit
NRZI Space
All ones
8-bit
FM0
All ones
8-bit
FM1
All zeros
8-bit
Manchester
101010...10
8-bit
Differential Manchester
All ones
8-bit
Содержание PowerQUICC MPC870
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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 ...
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