Multi-Tech Systems Receiver FIFO Interrupt Operation, Transmitter FIFO Interrupt Operation

Chapter 4 – SocketModem Parallel Interface – A Programmer's Descr iption
Multi-Tech Systems, Inc. SocketModem MT5600SMI Developer’s Guide 28
Receiver FIFO Interrupt Operation
Receiver Data Available Interrupt
When the FIFO mode is enabled (FCR0 = 1) and receiver interrupt (RX D ata Available) is enabled
(IER0 = 1), receiver interrupt operation is as follows:
1. The Receiver Data Available Flag (LSR0) is set as soon as a re ceived data character is
available in the RX FIFO. LSR0 is cleared when RX FIFO is empty.
2. The Receiver Data Available Interrupt code (IIR0-IIR4 = 4h) is set whenever the number of
received data bytes in the RX FIFO reaches the trigger level sp ecified by FCR6-FCR7 bits. It
is cleared whenever the number of received data bytes in the RX FIFO drops below the
trigger level specified by FCR6-FCR7 bits.
3. The HINT interrupt is asserted whenever the number of received data b ytes in the RX FIFO
reaches the trigger level specified by FCR6-FCR7 bits. HINT interrupt is de-asserted when
the number of received data bytes in the RX FIFO drops below the tr igger level specified by
FCR6-FCR7 bits.
Receiver Character Timeout Interrupts
When the FIFO mode is enabled (FCR0 = 1) and receiver interrupt (Re ceiver Data Available) is
enabled (IER0 = 1), receiver character timeout interrupt operati on is as follows:
1. A Receiver character timeout interrupt code (IIR0-IIR3 = Ch) is set if at least one received
character is in the RX FIFO, the most recent received serial character wa s longer than four
continuous character times ago (if 2 stop bits are specified, the second stop bit is included in
this time period), and the most recent host read of the RX FIFO was lo nger than four
continuous character times ago.
Transmitter FIFO Interrupt Operation
Transmitter Empty Interrupt
When the FIFO mode is enabled (FCR0 = 1) and transmitter interrupt (TX Buffer Empty) is enabled
(IER0 =1), transmitter interrupt operation is as follows:
1. The TX Buffer Empty interrupt code (IIR0-IIR3 = 2h) will occur when the TX Buffer is empty. It
is cleared when the TX Buffer is written to (1 to 16 characters) or the IIR i s read.
2. The TX Buffer Empty indications will be delayed 1 character t ime minus the last stop bit time
whenever the following occur: THRE = 1 and there have not been at lea st two bytes at the
same time in the TX FIFO Buffer since the last setting of THRE was set. The first transmitter
interrupt after setting FCR0 will be immediate.