APPENDIX C
GPS OPTION 14 IEEE-488 I/O INTERFACE
ASSEMBLY 55089 OR 55115
1.0 INTRODUCTION
This assembly is designed in accordance with the IEEE-488/1978 specification and is used to
provide the electrical interface between the GPS Time Code and Frequency Generator (TC &
FG) and the IEEE-488 bus.
When programmed as a listener, this assembly provides the capability to remotely control the TC
& FG. When programmed as a talker, this assembly provides the capability to output time,
status, location, etc. Five of the eight bus control lines (DAV, NRFD, NDAC, ATN and IFC) are
used in this option. EOI, SRQ and REN have no assigned function. The controller cannot
perform a serial poll of this assembly.
It is not recommended that the IEEE-488 and the RS-232 I/O be operated simultaneously.
1.1 INSTALLATION
This assembly is plugged into and works in conjunction with the motherboard option (GPS
Option 40) of the time code and frequency generator. Interconnection to the IEEE-488 bus is
provided through rear panel connector J13.Refer to the GPS Option Connection/Configuration
sheet in the User’s Guide.
1.2 OPERATION
The first step in using the IEEE-488 I/O port is to program/select the Device Address. The
current IEEE-488 address may be found by pressing the front panel MENU keypad switch until
the IEEE-488 screen (as shown below) is displayed on the LCD display.
<1> IEEE488 ADDR.17
If desired, the address may be changed by pressing the 1 key of the keypad, which causes the two
digits following ADDR. to change to “xx” prompting the user to enter a two digit address. A
leading zero is required if address is less than 10.
If a cold reset was performed at power up, the default address will be 17. The address can be
changed by closing (pushing down) rear panel DIP switch SW2, position 3. Watch the display,
and the address will increment at one second intervals.
When the desired address is reached, open (push up) DIP switch SW2, position 3. The Device
Address can also be selected via the RS-232 I/O port. The user inputs $CXX. (The XX
corresponds to a two digit device address number). The unit will respond with OK CR/LF
(carriage return/line feed).
C-36 ET6xxx ExacTime GPS TC & FG (Rev C) Symmetricom Inc
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