Multi-Tech Systems 92U09J14828 Manuel D’Utilisation
PART 3 – Analog SocketModems
Chapter 8 – SocketModem (MT9234SMI)
Multi-Tech Systems, Inc. Universal Socket Hardware Guide for Developers (S000342P)
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IIR – Interrupt Identification (Read Only)
Bits 6–7: (FIFO enabled bits). These bits will read a 1 if FIFO mode is enabled and the 16450 enable bit
is 0 (no force of 16450 mode).
Bits 4–5: Reserved and always read a 0.
Bits 1–3: Interrupt ID bits.
Bit 0:
Interrupt pending. If logic 0 (in default mode), an interrupt is pending.
When the host accesses IIR, the contents of the register are frozen. Any new interrupts will be recorded,
but not acknowledged during the IIR access. This requires buffering bits (0–3, 6–7) during IIR reads.
but not acknowledged during the IIR access. This requires buffering bits (0–3, 6–7) during IIR reads.
Interrupt Sources and Reset Control Table
Bit 3 Bit 2 Bit 1 Priority
Interrupt Source
Interrupt Reset Control
0
1
1
Highest
Overrun, parity, framing, error
or break detect bits set by
SocketModem Controller
or break detect bits set by
SocketModem Controller
Reading the LSR
0
1
0
2
nd
Received data trigger level
RX FIFO drops below trigger level
1
1
0
2
nd
Receiver time-out with data in
RX FIFO
RX FIFO
Read RX FIFO
0
0
1
3
rd
TX holding register empty
Writing to TX holding register or
reading IIR when TX holding register
is source of error
reading IIR when TX holding register
is source of error
0
0
0
4
th
MODEM status: CTS, DSR, RI
or DCD
or DCD
Reading the MSR
FCR – FIFO Control
Bits 6–7: Used to determine RX FIFO trigger levels.
Bit 5:
Bit 5:
Used to detect a change in the FCR.
Bit 4:
TX FIFO overrun bit.
Bit 3:
DMA mode select. Must be set to zero. When bit 3 is a 0, the 16450 mode is enabled which
does only single-byte transfers.
does only single-byte transfers.
Bit 2:
TX FIFO reset. This will cause TX FIFO pointer logic to be reset (any data in TX FIFO will be
lost). This bit is self clearing; however, a shadow bit exists that is cleared only when read by the
host, thus allowing the host to monitor a FIFO reset.
lost). This bit is self clearing; however, a shadow bit exists that is cleared only when read by the
host, thus allowing the host to monitor a FIFO reset.
Bit 1:
RX FIFO reset. This will cause RX FIFO pointer logic to be reset (any data in RX FIFO will be
lost). This bit is self clearing; however, a shadow bit exists that is cleared only when read by the
host, thus allowing the host to monitor a FIFO reset.
lost). This bit is self clearing; however, a shadow bit exists that is cleared only when read by the
host, thus allowing the host to monitor a FIFO reset.
Bit 0:
FIFO enable. The host writes this bit to logic 1 to put the block in FIFO mode. This bit must be a
1 when writing other bits in this register or they will not be programmed. When this bit changes
state, any data in the FIFOs or the RBR and THR registers will be lost and any pending
interrupts are cleared.
1 when writing other bits in this register or they will not be programmed. When this bit changes
state, any data in the FIFOs or the RBR and THR registers will be lost and any pending
interrupts are cleared.
Bit 7
Bit 6
16 Deep FIFO Trigger Levels
(# of bytes) Default
(# of bytes) Default
0
0
1
0
1
4
1
0
8
1
1
14
LCR – Line Control
Bit 7:
Divisor latch access bit. This bit allows the host, access to the divisor latch. Under normal
circumstances, the bit is set to 0 (provides access to the RX and TX FIFOs at address 0). If the
bit is set to 1, access to transmitter, receiver, interrupt enable, and modem control registers is
disabled. In this case, when an access is made to address 0, the divisor latch least (DLL)
significant byte is accessed. Address 1 accesses the most significant byte (DLM). Address 7
accesses the DLX divisor latch register. Address 4 accesses the MCX status/control register.
circumstances, the bit is set to 0 (provides access to the RX and TX FIFOs at address 0). If the
bit is set to 1, access to transmitter, receiver, interrupt enable, and modem control registers is
disabled. In this case, when an access is made to address 0, the divisor latch least (DLL)
significant byte is accessed. Address 1 accesses the most significant byte (DLM). Address 7
accesses the DLX divisor latch register. Address 4 accesses the MCX status/control register.
Bit 6:
Used to denote a host-generated set break condition.
Bits 0,1,3,4,5: Used only in parity bit generation for the 7 bit data byte case. Bits 0 and 1 are used for
word length select (b0 = 0 and b1 = 1 is used for 7 bit data). Bit 3 is parity enable. Bit 4 is even
parity select. Bit 5 is stick parity.
parity select. Bit 5 is stick parity.