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ADVANCED MICRO SYSTEMS, INC. SERIAL INTERFACE
15
Overview
This Application covers the serial communication design for ADVANCED MICRO SYSTEMS, INC. (AMS)
intelligent control products. These products include complete packaged systems, OEM boards, sub-
assemblies, and I.C.’s. The basic design has remained constant over 20 years. All AMS products are based
on the same core micro-controller family, which contain two-way serial communication using the standard
ASCII characters used in virtually all computers.
Only two signals are used, TXD (transmitted data) and RXD (received data). The hardware interface for the
two signals is one of two industry standards, either RS-232 or RS-422. These standards describe the
physical wire layout and signal voltage swings. The brief descriptions here are those relevant to AMS
product communications and do not include DTR, DSR, CTS, RTS, etc.
RS-232
Introduced in 1962, RS-232 has been widely used throughout the industry. This single ended transmission is
useful only for short distances. The connector is either a 9 or 25 pin “D” connector. RS-232 includes a 3-wire
interface using RXD, TXD and ground.
Typical voltage swings are –12 volts to +12 volts. The relatively high impedance and low speed limit both
baud rates and wire length. In non-hostile environments and limited distance communications it will operate
with 0 to +5 volt swing.
RS-232 can operate with one serial driver and one serial receiver at a maximum of 20k baud. For serious
designs (even with one axis) we recommend the RS-422 mode of operation.
Stand-alone Operation
All AMS controllers include “non-volatile memory” to hold program sequences that, once inserted, can be
triggered at power up via a switch closure or pulse input. Since the purpose of the serial interface in this
application is only to enable insertion of the command sequences, RS-232 is adequate.
RS-422
RS-422 is a newer transmission system that incorporates a 2 wire per signal differential standard that is faster
and useful at up to 400 feet at 1M baud or 4,000 feet at 100K baud. This 5-wire signal, full duplex interface
includes RX+, RX-, TX+, TX- and Ground. This system is capable of driving up to 32 receivers (motor
control axis) on a single “drop” bus. Voltage swings are 0 to +5 volts.
While not recommended, the RS-422 line receivers will withstand RS-232 levels. RS-232 receivers work with
the lower 5-volt swing, permitting both single ended and differential operation.
RS-232 Hardware
There are two ways to configure AMS RS-232 products. The basic connection is single axis mode with a
straight RS-232 connection using a SIN-7 serial adapter.
SIN-7 / SIN-9 RS-232 Serial Adapter
The SIN-7 is a DB-25 to RJ-45 adapter for single axis, RS-232 communication applications. The SIN-9 is a 9-
pin version. These converters facilitate connection between a standard computer “D” connector output and
AMS’ RJ-45 connector inputs.
Features include:
• Connects computer or terminal to axis
• Standard 25 pin or 9 pin connector for COM port
• Passive - no power required