Technics MT5634SMI-34 manual RBR Receive Buffer RX FIFO, THR Transmit Holding Register TX FIFO

Chapter 4 – SocketModem Parallel Interface – A Programmer’s Description

RBR Receive Buffer (RX FIFO)

All eight bits are used for receive channel data (host read/data in; host write/data out). The three error bits per byte are copied into bits 2, 3, and 4 of the LSR during each host I/O read; therefore, they are available for monitoring on a per-byte basis.

THR Transmit Holding Register (TX FIFO)

All eight bits are used for transmit channel data (host write/data out; host read/data in).

IER Interrupt Enable

Bits 4–7:Reserved and will always read 0.

Bits 0-3: Set by host software only and cleared by software control or host reset.

Bit 3: Enables modem status IRQ. If bits 0–3 of the MSR are set and this bit is set to 1 (enabled), a host interrupt is generated.

Bit 2: Enables receive line status IRQ. If bits 1–4 (overrun, parity, framing, break errors) of the LSR are set and this bit is set to a logic 1, a host interrupt is generated.

Bit 1: Enables transmit holding register IRQ. If bit 5 (transmit holding register empty) of the LSR is set and this bit is set to a 1, a host interrupt is generated.

Bit 0: Enables received data available IRQ. If bit 0 (data ready) of the LSR is set and this bit is set to a 1, a host interrupt is generated.

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.

Bit 3	Bit 2	Bit 1	Priority	Interrupt Source	Interrupt Reset Control
0	1	1	Highest	Overrun, parity, framing, error	Reading the LSR
				or break detect bits set by
				SocketModem Controller
0	1	0	2nd	Received data trigger level	RX FIFO drops below trigger
					level
1	1	0	2nd	Receiver time-out with data in	Read RX FIFO
				RX FIFO
0	0	1	3rd	TX holding register empty	Writing to TX holding register
					or reading IIR when TX
					holding register is source of
					error
0	0	0	4th	MODEM status: CTS, DSR,	Reading the MSR
				RI or DCD

SocketModem Global MT5634SMI Developer’s Guide 19