XC886/888CLM
Serial Interfaces
User’s Manual
12-42
V1.3, 2010-02
Serial Interfaces, V 1.0
A
Phase Error
(master or slave mode) is detected when the incoming data at pin MRST
(master mode) or MTSR (slave mode), sampled with the same frequency as the module
clock, changes between one cycle before and two cycles after the latching edge of the
shift clock signal SCLK. This condition sets the error flag CON.PE and, when enabled
via CON.PEN, sets the EIR.
Note: When receiving and transmitting data in parallel, phase error occurs if the baud
rate is configured to
f
hw_clk
/2.
A
Baud Rate Error
(slave mode) is detected when the incoming clock signal deviates
from the programmed baud rate by more than 100%, i.e., it is either more than double or
less than half the expected baud rate. This condition sets the error flag CON.BE and,
when enabled via CON.BEN, sets the EIR. Using this error detection capability requires
that the slave’s baud-rate generator be programmed to the same baud rate as the
master device. This feature detects false, additional or missing pulses on the clock line
(within a certain frame).
Note: If this error condition occurs and bit CON.AREN = 1, an automatic reset of the
SSC will be performed. This is done to re-initialize the SSC if too few or too many
clock pulses have been detected.
Note: This error can occur after any transfer if the communication is stopped. This is the
case due to the fact that the SSC module supports back-to-back transfers for
multiple transfers. In order to handle this, the baud rate detector expects
immediately after a finished transfer, the next clock cycle for a new transfer.
A
Transmit Error
(slave mode) is detected when a transfer was initiated by the master
(SS_CLK gets active), but the transmit buffer TB of the slave had not been updated since
the last transfer. This condition sets the error flag CON.TE and the EIR, when enabled
via CON.TEN. If a transfer starts without the transmit buffer having been updated, the
slave will shift out the ‘old’ contents of the shift register, which normally is the data
received during the last transfer. This may lead to corruption of the data on the
transmit/receive line in half-duplex mode (open drain configuration) if this slave is not
selected for transmission. This mode requires that slaves not selected for transmission
only shift out ones; that is, their transmit buffers must be loaded with ‘FFFF
H
’ prior to any
transfer.
Note: A slave with push/pull output drivers not selected for transmission, will normally
have its output drivers switched off. However, in order to avoid possible conflicts
or misinterpretations, it is recommended to always load the slave's transmit buffer
prior to any transfer.
The cause of an error interrupt request (receive, phase, baud rate or transmit error) can
be identified by the error status flags in control register CON.
Note: The error status flags CON.TE, CON.RE, CON.PE, and CON.BE are not reset
automatically upon entry into the error interrupt service routine, but must be
cleared by software.
*
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