
12-62
DSP56853/854/855/857/858 User’s Manual
MOTOROLA
Preliminary
Interrupt Operation Description
12
12.11 Interrupts
The ESSI can generate up to six interrupt vectors, listed in Table 12-26. 12.12 Interrupt Operation Description
12.12.1 Receive Data With Exception
This interrupt can occur when receive interrupts are enabled via the RIE bit of the SCR2
register. When a data word is ready to transfer from the RXSR register to the SRX register
and the previous SRX register data has not yet been read, the ROE bit is set and the
exception interrupt will occur instead of the normal receive data interrupt. When the
receive FIFO is enabled this interrupt will not occur until the RFF bit has been set,
indicating the FIFO is full. The ROE bit is cleared when the SSR is read verifying the
ROE bit is set before reading the SRX register data.
12.12.2 Receive Data (RX)
This interrupt can occur when receive interrupts are enabled via the RIE bit of the SCR2
register. When a data word is ready to transfer from the RXSR register to the SRX
register, and the ROE bit is not set, an interrupt will occur indicating received data is
available for processing. When the Receive FIFO is enabled, this interrupt will not occur
until the Receive Watermark level of the FIFO is reached. If the FIFO is not enabled, an
interrupt will occur for each data word received. This interrupt is cleared by reading the
SSR, verifying the RDR bit is set before reading the SRX register data.
12.12.3 Receive Last Slot (RLS)
This interrupt occurs when the ESSI:
Is in the Network mode
Has been enabled via the RLIE bit of the SCR3 register
Table 12-26.
Interrupt Summary
Interrupt
Source
Description
INTR + $0
Receiver
Receive data with exception
INTR + $2
Receiver
Receive data
INTR + $4
Receiver
Receive last slot interrupt. This interrupt may not be present in all
implementations of the ESSI.
INTR + $6
Transmitter
Transmit data with exception
INTR + $8
Transmitter
Transmit data
INTR + $10
Transmitter
Transmit last slot interrupt. This interrupt may not be present in all
implementations of the ESSI.