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Chapter 4 – SocketModem Parallel Interface – A Programmer's Description
Multi-Tech Systems, Inc. SocketModem MT5600SMI Developer’s Guide 18
Chapter 4 – SocketModem Parallel
Interface – A Programmer’s
Description
SocketModem Parallel Interface
The modem supports a 16550A interface in parallel interface versions. The 16550A interface can operate
in FIFO mode or non-FIFO mode. Non-FIFO mode is the same as the 16450 interface operation. FIFO
mode’s unique operations are described in this chapter.
Overview
The modem emulates the 16450/16550A interface and includes both a 16-byte receiver data first-in first-
out buffer (RX FIFO) and a 16-byte transmit data first-in first-out buffer (TX FIFO).
FIFO Mode Selected
When FIFO mode is selected in the FIFO Control Register (FCR0 = 1), both FIFOs are operative.
Furthermore, when FIFO mode is selected, DMA operation of the FIFO can also be selected (FCR3 = 1).
FIFO Mode Not Selected
When FIFO mode is not selected, operation is restricted to a 16450 interface operation.
Receive Data
Received Data is read by the host from the Receiver Buffer (RX Buffer). The RX Buffer corresponds to
the Receiver Buffer Register in a 16550A device. In FIFO mode, the RX FIFO operates transparently
behind the RX Buffer. Interface operation is described with reference to the RX Buffer in FIFO and non-
FIFO modes.
Transmit Data
Transmit Data is loaded by the host into the Transmit Buffer (TX Buffer). The TX Buffer corresponds to
the Transmit Holding Register in a 16550A device. In FIFO mode, the TX FIFO operates transparently
behind the TX Buffer. Interface operation is described with reference to the TX Buffer in both FIFO and
non-FIFO modes.
Note
The parallel interface registers and the corresponding bit assignments are shown in Table 4–1.