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11-182 SA-1100
Developer’s Manual
Peripheral Control Module
11.12.12.5 Receive FIFO Service Request Flag (RFS) (read-only, maskable
interrupt)
The receive FIFO service request flag (RFS) is a read-only bit that is set when the receive FIFO is nearly
filled and requires service to prevent an overrun. RFS is set whenever the receive FIFO has four or more
entries of valid data (half-full or more), and is cleared when it has three or fewer (less than half-full)
entries of data. When the RFS bit is set, an interrupt request is made unless the receive FIFO interrupt
request enable (RIE) bit is cleared. The state of RFS is also sent to the DMA controller, and can be used
to signal a DMA service request. Note that RIE has no effect on the generation of the DMA service
request. After the DMA or CPU fills the FIFO such that four or more locations are filled within the
receive FIFO, the RFS flag (and the service request and/or interrupt) is automatically cleared.
11.12.12.6 Receiver Overrun Status (ROR) (read/write, nonmaskable interrupt)
The receiver overrun status bit (ROR) is a read/write bit that is set when the receive logic attempts
to place data into the receive FIFO after it has been completely filled. Each time a new piece of
data is received, the set signal to the ROR 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 ROR bit is set, an interrupt request is made.
The following table shows the bit locations corresponding to the status and flag bits within the SSP
status register. All bits are read-only except ROR, which is read/write. Writes to TNF, RNE, BSY, TFS,
and RFS have no effect. The reset state of ROR is unknown (indicated by a question mark) and must be
initialized before enabling the SSP. Note that writes to reserved bits are ignored and reads return zeros.
Address: 0h 8007 0074 SSP Status Register: SSSR
Read/Write &
Read-Only
Bit 1514131211109876543210
Reserved ROR RFS TFS BSY RNE TNF Res
Reset000000000?000010
Bit Name Description
0 — Reserved.
1TNF
Transmit FIFO not full (read-only).
0 – Transmit FIFO is full.
1 – Transmit FIFO is not full.
2 RNE
Receive FIFO not empty (read-only).
0 – Receive FIFO is empty.
1 – Receive FIFO is not empty.
3BSY
SSP busy flag (read-only).
0 – SSP is idle or disabled.
1 – SSP is currently transmitting and/or receiving a frame (no interrupt generated).
4 TFS
Transmit FIFO service request (read-only).
0 – Transmit FIFO is more than half-full (five or more entries filled) or SSP disabled.
1 – Transmit FIFO is half-full or less (four or fewer entries filled) and SSP operation is
enabled, DMA service request signalled, interrupt request signalled if not masked (if TIE=1).
5RFS
Receive FIFO service request (read-only).
0 – Receive FIFO is less than half-full (three or fewer entries filled) or SSP disabled.
1 – Receive FIFO is half-full or more (four or more entries filled) and SSP operation is
enabled, DMA service request signalled, interrupt request signalled if not masked (if RIE=1).
6ROR
Receive FIFO overrun.
0 – Receive FIFO has not experienced an overrun.
1 – Receive logic attempted to place data into receive FIFO while it was full, request interrupt.
15..7 — Reserved.