AR-B1462 User¡¦s Guide

2-6

2.6 SERIAL PORT
The ACEs (Asynchronous Communication Elements ACE1 to ACE4) are used to convert parallel data to a serial
format on the transmit side and convert serial data to parallel on the receiver side. The serial format, in order of
transmission and reception, is a start bit, followed by five to eight data bits, a parity bit (if programmed) and one,
one and half (five-bit format only) or two stop bits. The ACEs are capable of handling divisors of 1 to 65535, and
produce a 16x clock for driving the internal transmitter logic.
Provisions are also included to use this 16x clock to drive the receiver logic. Also included in the ACE a completed
MODEM control capability, and a processor interrupt system that may be software tailored to the computing time
required handle the communications link.
The following table is summary of each ACE accessible register
DLAB Port Address Register
Receiver buffer (read)0base + 0
Transmitter holding register (write)
0base + 1 Interrupt enable
Xbase + 2 Interrupt identification (read only)
Xbase + 3 Line control
Xbase + 4 MODEM control
Xbase + 5 Line status
Xbase + 6 MODEM status
Xbase + 7 Scratched register
1base + 0 Divisor latch (least significant byte)
1base + 1 Divisor latch (most significant byte)
Table 2-6 ACE Accessible Registers

(1) Receiver Buffer Register (RBR)

Bit 0-7: Received data byte (Read Only)

(2) Transmitter Holding Register (THR)

Bit 0-7: Transmitter holding data byte (Write Only)

(3) Interrupt Enable Register (IER)

Bit 0: Enable Received Data Available Interrupt (ERBFI)
Bit 1: Enable Transmitter Holding Empty Interrupt (ETBEI)
Bit 2: Enable Receiver Line Status Interrupt (ELSI)
Bit 3: Enable MODEM Status Interrupt (EDSSI)
Bit 4: Must be 0
Bit 5: Must be 0
Bit 6: Must be 0
Bit 7: Must be 0

(4) Interrupt Identification Register (IIR)

Bit 0: “0” if Interrupt Pending
Bit 1: Interrupt ID Bit 0
Bit 2: Interrupt ID Bit 1
Bit 3: Must be 0
Bit 4: Must be 0
Bit 5: Must be 0
Bit 6: Must be 0
Bit 7: Must be 0