Measurement Computing COM232/8AT - Manual (Page 8)

8 COM232/8AT User’s Guide March 1998 1000-0901, rev 1.1
If you need to connect two DTEs together, you must make use of a customized cable known as a NULL MODEM or
MODEM Eliminator. A typical DTE-to-DTE cable is as follows:
Register Definitions
This section provides a brief summary of the 16550 ACE internal registers. The registers are addressed
as indicated in the following table.
Note: The 16550 Asynchronous Communications Element (ACE) enters character mode on reset.
When the 16550 ACE is in character mode it appears as a 16450 ACE to the software.
16550 ACE Internal Register Map
DLAB
(see note)
A2 A1 A0 Description
0 0 0 0 Receive Buffer (read only)
Transmitter Holding Register (write only)
0 0 0 1 Interrupt Enable
x 0 1 0 Interrupt Identification (read only)
FIFO Control (write only)
x 0 1 1 Line Control
x 1 0 0 MODEM Control
x 1 0 1 Line Status
x 1 1 0 MODEM Status
x 1 1 1 Scratch
1 0 0 0 Divisor Latch (LSB)
1 0 0 1 Divisor Latch (MSB)
Note: DLAB is accessed through the Line Control Register.
Interrupt Enable Register
The bit definitions for the Interrupt Enable Register are as follows:
Interrupt Enable Register Definitions
D7 0
D6 0
D5 0
D4 0
D3 EDSSI MODEM Status
D2 ELSI Receiver Line Status
D1 ETBEI Transmitter Holding Register Empty
D0 ERBFI Received Data Available