
User Notes
MOTOROLA
Enhanced Synchronous Serial Interface (ESSI)
12-63
Preliminary
12
The last slot of the frame has ended
The RLS bit is also set at this time. This interrupt is generated regardless of the receive
mask register setting. This interrupt and the RLS bit are cleared by writing a 1 to the RLS
bit of the ESSI Status Register (SSR).
12.12.4 Transmit Data With Exception
This interrupt can occur when transmit interrupts are enabled via the TIE bit of the SCR2
register. When it is time to transfer data to the TXSR and data is not available in enabled
STX or TXFIFO, the TUE status bit is set and the transmit data exception interrupt occurs.
The TUE bit, and its interrupt, is cleared when the SSR is read then written to all the
transmit data registers of the enabled transmitters or when written to the STSR.
12.12.5 Transmit Data (TX)
This interrupt can occur when transmit interrupts are enabled via the TIE bit of the SCR2
register. When data is transferred to the TXSR this interrupt will occur if more data is
needed by any enabled transmitter.
If the transmit FIFO is not enabled this interrupt will occur for each data word transmitted.
However, when the transmit FIFO is enabled, the interrupt will not occur until the
Transmit Watermark level is reached. This interrupt is cleared by reading the SSR and
writing data to the enabled STX registers. The interrupt may also be cleared by writing to
the STSR.
12.12.6 Transmit Last Slot (TLS)
This interrupt occurs when the ESSI is in the Network mode at the beginning of the last
slot of the transmit frame. The TLS bit is also set at this time. This exception occurs
regardless of the Transmit Mask Register setting. This interrupt and the TLS bit are
cleared by writing a 1 to the TLS bit of the SSR.
12.13 User Notes
12.13.1 External Frame Sync Setup
When using external frame syncs, there must be at least four clocks after enabling the
transmitter/receiver and before the first frame sync.
12.13.2 Maximum External Clock Rate
The maximum allowable rate for an external clock source is one fourth of the peripheral
clock.