Motorola DragonBall MC9328MX1 Reference Manual page 700

SmartCard Interface Module (SIM)
Table 25-14. Receive Status Register Description (Continued)
Name
RDRF Receive Data Register Full—Indicates whether the SIM
Bit 2 receive FIFO has reached the threshold level set by RDT in
the RCV_THRESHOLD register. The RDRF flag is set any
time the number of unread bytes in the receive FIFO is equal
to or greater than the value set by RDT. The flag is cleared by
reading enough bytes out of the receive FIFO to bring the
number of bytes left in the FIFO below the RDT level. Another
way to clear the flag is to set the RDT level higher than the
number of unread bytes currently in the FIFO. The RDRF flag
creates an interrupt when the RIM bit in the INT_MASK
register is cleared.
RFD Receive FIFO has Unread Data—Indicates that there is at
Bit 1 least one unread byte in the receive data FIFO. Cleared only
by reading all bytes out of the receive FIFO. The RFD bit
cannot create an interrupt. Normally, the SIM triggers the
interrupt with RDRF, and software uses RFD to read all of the
bytes out of the receive FIFO.
OEF Overrun Error Flag—Indicates that the SIM was unable to
Bit 0 store received data because there already were 32 unread
bytes in the FIFO. This does not necessarily indicate that data
has been lost. When the ONACK bit in the CNTL register is
set, a NACK pulse is generated on bytes that would otherwise
cause a loss of data due to a full FIFO. These bytes must be
retransmitted by the SmartCard which implies that no data
has actually been lost. In this case, the OEF flag is just an
indicator that this situation has occurred which may be helpful
in system debug. When ONACK is not set, a set OEF flag
indicates a loss of data because all bytes received with the
OEF flag set are lost (including the byte that caused the bit to
set). The OEF flag causes an interrupt when the OIM bit is set
in the INT_MASK register. The OEF flag is a
write-one-to-clear bit.
25-30
Description
MC9328MX1 Reference Manual
Settings
0 = Number of unread bytes in
receive buffer < value set by
RDT
1 = Number of unread bytes in
receive buffer >= value set by
RDT
0 = There are no unread bytes in the
receive FIFO
1 = There is at least one unread
byte in the receive FIFO
0 = No overrun error has occurred
1 = A byte was received when the
received FIFO was already full
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