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SA-1100 Developer’s Manual 11-165
Peripheral Control Module
11.12.6.7 Telecom Transmit FIFO Underrun Status (TTU) (read/write,
nonmaskable interrupt)
The telecom transmit FIFO underrun status bit (TTU) is set when the telecom transmit logic
attempts to fetch data from the FIFO after it has been completely emptied. When an underrun
occurs, the telecom transmit logic continuously transmits the last valid telecom value, which was
transmitted before the underrun occurred. Once data is placed in the FIFO and it is transferred
down to the bottom, the telecom transmit logic uses the new value within the FIFO for
transmission. When the TTU bit is set, an interrupt request is made.
11.12.6.8 Telecom Receive FIFO Overrun Status (TRO) (read/write,
nonmaskable interrupt)
The telecom receive FIFO overrun status bit (TRO) is set when the telecom receive logic places
data into the telecom receive FIFO after it has been completely filled. Each time a new piece of
data is received, the set signal to the TRO status bit is asserted, and the newly received data is
discarded. This process is repeated for each new piece of data received until at least one empty
FIFO entry exists. When the TRO bit is set, an interrupt request is made.
11.12.6.9 Audio Transmit FIFO Not Full Flag (ANF) (read-only, noninterruptible)
The audio transmit FIFO not full flag (ANF) is a read-only bit that is set whenever the audio
transmit FIFO contains one or more entries that do not contain valid data and is cleared when the
FIFO is completely full. This bit can be polled when using programmed I/O to fill the audio
transmit FIFO over its halfway mark. This bit does not request an interrupt.
11.12.6.10 Audio Receive FIFO Not Empty Flag (ANE) (read-only,
noninterruptible)
The audio receive FIFO not empty flag (ANE) is a read-only bit that is set whenever the audio
receive FIFO contains one or more entries of valid data and is cleared when it no longer contains
any valid data. This bit can be polled when using programmed I/O to remove remaining bytes of
data from the receive FIFO because DMA service and CPU interrupt requests are made only when
four or more bytes reside within the FIFO (3, 2, or 1 bytes may remain at the end of a frame). This
bit does not request an interrupt.
11.12.6.11 Telecom Transmit FIFO Not Full Flag (TNF) (read-only,
noninterruptible)
The telecom transmit FIFO not full flag (TNF) is a read-only bit that is set whenever the telecom
transmit FIFO contains one or more entries that do not contain valid data and is cleared when the
FIFO is completely full. This bit can be polled when using programmed I/O to fill the telecom
transmit FIFO over its halfway mark. This bit does not request an interrupt.