Equipment Overview; Tty/Eia Terminal Interface Module - Texas Instruments 990 Maintenance Manual

J}l~ _ _ _ _ _ _ _
~
945408-9701
SECTION I
GENERAL DESCRIPTION
1.1 GENERAL
The Teletypewriter/Electronic Industries Association (TTY /EIA) Terminal Interface Module (fig-
ure 1-1) provides a communication path from Texas Instruments Series 990 Computers to
peripheral devices that operate from either a current loop interface or an interface that conforms
to EIA Standard RS-232C. The TTY /EIA module can be wired for transmit and receive rates
ranging from 7 5 to 9600 baud, and character code formats of 10 or 11 bits. Typical devices
which can interface with the computer through this module include Texas Instruments Model
733 ASR or 733/743 KSR Data Terminals, Texas Instruments Model 306 and 588 Line Printers,
and Bell 103 (A or F) or 202 (C or D) data sets, or their equivalents.
1.2 EQUIPMENT OVERVIEW
Figure 1-2 is a simplified diagram of the TTY /EIA module. The module consists of transmit
logic, receive logic, and diagnostic logic. The transmit and receive logic can be exercised
simultaneously to achieve full duplex operation. Module timing is accomplished by a 4-MHz
oscillator and a group of counters that provide a jumper-selected divide network necessary for
generating the desired transmit/receive frequency. Prior to data transmission by the computer,
Figure 1-1. TTY/EIA Terminal Interface Module
1
Digital Systems Division