Specifications

Theory of Operation
156 025-9035AA
Dual Trunk Card — 4-Wire E&M (702-9318)
This card is physically very similar to the standard Dual Trunk card. In fact, it uses the
same printed circuit board. The difference is that it also has a daughter board mounted on
it that provides the appropriate interface for 4-wire audio.
This card is only used with 4-wire E&M trunk lines. The control functions of the “E” and
“M” leads are the same as they were for a 2-wire E&M trunk. The 4-wire audio allows the
use of a separate pair for both the receive and transmit audio. This means better audio
during calls and less work installing and maintaining the line.
Unlike the standard Dual Trunk card, this card may not be used for any other line type.
Multiport Serial Card (702-9191)
The Multiport card is basically a Dual Trunk with the telephone line portions deleted, and
serial ports substituted.
This card handles from 1 to 8 serial ports. (See separate section for installation &
operation information). The incoming serial lines for the ports come through MC14506
RS-232 driver chips, which provide buffering and signal conditioning for both in- and out-
bound signals. Two data and two handshaking lines are used for each port (although the
software does not currently use the handshaking lines).
The serial lines then go from these chips to 2681 Dual UART chips. These DUARTs have
two independent UARTs (Universal Asynchronous Receiver/ Transmitter) in them. Each
port can have its own baud rate, word size, etc.
These DUART chips then interface directly to the Multiport card microprocessor's data,
address, and control busses.
The Multiport card's microprocessor is comprised of a Motorola 68HC11 processor, static
RAM, EPROM, and various “glue” chips.
The interface to the main paging system is through a dual-port RAM, the same as the Dual
trunks.