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MibSPI Operation Modes
Multi-Buffer Serial Peripheral Interface (MibSPI) (SPNU217B)
23
2.14
Lock Transmission
In order to be accessed, some slave device require, a command followed by
data. In this case, the SPI transaction should not be interrupted by another
group transfer. The LOCK bit within each buffer allows consecutive transfer
to happen without interruption by another group transfer.
2.15
Hold Chip-Select Active (Master only)
There are slave devices available that require the chip-select signal to be
held continuously active during several consecutive data word transfers.
Other slave devices require the chip-select signal to be deactivated between
consecutive data word transfers. Each MibSPI buffer can be individually
initialized for either of the two modes via the CSHOLD bit in its control field.
If the CSHOLD bit is set in the control field of a buffer, the chip-select signal
will not be deactivated until the next control information is loaded with new
chip-select information. Since the chip-select is maintained active between
two transfers, the chips-select hold delay is not applied at the end of the
current transaction, nor is the chip-select set-up time delay applied at the
beginning of the following transaction. However, the wait delay could be still
applied between the two transactions, if the bit WDEL is set within the control
field.
Note:
When CSHOLD is active, no transmission interruptions are allowed. The
LOCK bit does not keep the CS active.
2.16
Detection of Slave De-synchronization (Master only)
When a slave supports generation of an enable signal (ENA) a de-
synchronization can be detected. With the enable signal, a slave indicates to
the master that it is ready to exchange data. A de-synchronization can occur
if one or more clock edges are missed by the slave. In this case, the slave
may block the SOMI line until it detects clock edges corresponding to the next
data word. This would corrupt the data word of the de-synchronized slave and
the consecutive data word. A configurable 8-bit time-out counter, which is
clocked with SPI clock, is implemented to detect this slave malfunction. After
the transmission has finished (end of last bit transferred: either last data bit or
parity bit) the counter is started. If the ENAble signal generated by the slave
isn’t becoming inactive before the counter expires the DESYNC flag is set
and a interrupt is asserted if enabled. The DESYNC flag is set as well if the
slave deactivates the ENAble signal before the last bit is transferred.
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