Specifications

APPENDIX B. IMPLEMENTATION DETAILS 34
For this project we use to types of clock cards: master cards and slave cards. The only
difference between them is that the master cards have the Write Down Output enabled.
The connectors of the clock cards are shown in the figure Figure B.1.
24
Port #1 Port #2 Port #3 Port #4
Port #2 − Write down (OUTPUT) − only for master card
Port #3 − 1 Hz PPS signal from GPS (input)
Port #4 − Write down (input)
Port #1 − 10 MHz clock from GPS (input)
Figure B.1: Connectors on the clock board
A description of the ports of the clock cards is given below.
WRITE DOWN (input) For the special commands from the master card
GPS PPS (input) The 1Hz signal from the GPS card (PPS = Pulse Per Sec ond)
CLOCK (input) The 10MHz clock from the GPS
WRITE DOWN (OUTPUT) Active only for master clock cards. It sends commands
to slaves and is connected to all the boards.
The type of a port (input or output) can be modified by making some hardware modifica-
tions on the board. There are a lot of clock boards available, but most of them are not yet
modified to work with the new configuration.
NOTE: Brian Martin’s logbook shows information about the jumper settings on the clock
cards. There is also some concise info on the I/O configuration of the board connectors in
Catalin Meirosu’s logbook.
There are already 4 clock cards modified for use with the GPS. Their numbers are noted
in Catalin’s logbook. More cards will need to be mo dified to test a complete setup. The
modified boards are:
• board #37 - master clock card, works fine - was used for initial tests (it was also used
by Miron).
• board #33 - slave clock card, works fine - also used by Miron
• board #24 - master clock card - recently modified - some problems were observed
with the continuous GPS testing (strange numbers appear from time to time).
• board #31 - master clock card - has the same problems as #24