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Architecture
1438
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Serial Peripheral Interface (SPI)
29.2.20.4 SPI 5-Pin Mode
shows the T2CDELAY, T2EDELAY, and WDELAY delays in SPI 5-pin master mode.
•
In CASE1, the SPIx_ENA is deasserted during the T2CDELAY period. However the T2CDELAY period
proceeds to completion(a), the T2EDELAY period is skipped (if enabled) and the WDELAY period
begins immediately (b) (if enabled). The next transfer is initiated as soon as the slave asserts
SPIx_ENA again.
•
In CASE2, the SPIx_ENA signal is deasserted by the slave during the T2EDELAY period (d) which
begins upon the completion of the T2CDELAY period (c). The deassertion of the SPIx_ENA causes
the T2EDELAY period to terminate early and the WDELAY period (e) begins immediately (if enabled)
after the T2EDELAY period terminates. The next transfer is initiated as soon as the slave asserts
SPIx_ENA again.
•
In CASE3, the SPIx_ENA signal is deasserted by the slave during the WDELAY period (h) which
begins upon the completion of the T2CDELAY period (f) and T2EDELAY period (g). As a result the
DESYNC error is set at the end of the T2EDELAY period (g). However since the SPIx_ENA is
deasserted during the WDELAY period (h), the master delays the next transfer until the SPIx_ENA is
asserted again.
•
In CASE4, the SPIx_ENA signal is not deasserted until after the completion of the T2CDELAY (j),
T2EDELAY (k) and WDELAY (m) (if enabled) periods. The DESYNC error is set at the end of the
T2EDELAY period (k). However in this case the master begins the next transfer immediately after it is
initiated and ignores the SPIx_ENA during the transfer even if it is subsequently deasserted.
If the T2EDELAY delay period is disabled then the DESYNC error is not set. The SPI master behavior
in this case depends on whether the SPIx_ENA gets deasserted during the T2CDELAY period
(CASE1), WDELAY period (CASE3) or after the WDELAY period completes (CASE4).
If the slave deasserts the SPIx_ENA signal before the completion of the configured master delays
(T2CDELAY, T2EDELAY, WDELAY) then the master delays the next transfer until the slave asserts
the SPIx_ENA again. However if the slave delays the SPIx_ENA deassertion until after the completion
of the configured master delays then the master begins the next transfer immediately after it is initiated
and ignores the SPIx_ENA during the transfer even if it is subsequently deasserted.
shows the C2TDELAY and C2EDELAY in SPI 5-pin master mode.
•
In CASE1, the SPIx_ENA signal is asserted during the C2TDELAY period (a). However the
C2TDELAY period proceeds to completion(a), the C2EDELAY period is skipped (if enabled) and the
master begins generating the SPI clock for transmission.
•
In CASE2, the SPIx_ENA signal is asserted during the C2EDELAY period (d) which begins upon the
completion of C2TDELAY period (c). The assertion of the SPIx_ENA causes the C2EDELAY period to
terminate early and the master begins generating the SPI clock for transmission.
•
In CASE3, the SPIx_ENA signal is not asserted until after the completion of the C2TDELAY (f) and
C2EDELAY (g) periods. The TIMEOUT error is set at the end of the C2EDELAY period (g). The master
deasserts the SPIx_SCS[n] signal immediately and clears the current transmit request.
If the C2EDELAY delay period is disabled then the SPI master behavior depends on whether the
SPIx_ENA gets asserted during the C2TDELAY period (CASE1) or after the C2TDELAY period
completes (CASE2). In latter case there is no limit on how long the master will wait for the slave to
respond with SPIx_ENA asserted and hence there is no limit on period 'd' shown in CASE2. Thus
when C2EDELAY period is disabled the TIMEOUT error is not set.