FIFO DATA PACKETS
Symmetricom, Inc.
bc620/627AT Time and Frequency Processor
4-15
4.1.14 PACKET “P” - PATH SELECTION
The term “path selection” might more appropriately be called switch selection or option control.
The purpose of this packet is to create branch points in the bc620 firmware. The path packet
contains two data bytes, each byte controls four switches, and each switch is assigned to a
particular bit in the lower 4 bits of each byte. The upper four bits of each byte are set to 3. The
default settings set all switches to 0
except that
the diagnostics bit which is set to 1. The format
is as follows:
byte 1
SOH.
byte 2
“P.”
byte 3
Data A (see below).
byte 4
Data B (see below).
byte 5
ETB.
Data A:
Bit 0: 0 = disable FIFO echo 1 = enable FIFO echo.
Bit 1: 0 = UTC Time 1 = GPS Time <1>.
Bit 2: 0 = Dynamics Code to Static 1 = Dynamics Code to Non-static <2>.
Bit 3: 0 = Packed BCD Time Format 1 = long second format <3>.
<1>
UTC time = GPS time - GPS leap seconds. GPS time does not use GPS leap
seconds.
<2>
Auto set of GPS dynamics code to Static by bc627AT after initialization to GPS.
Allows accurate time keeping without a full position fix for stationary users.
<3>
Major time over PCbus is binary seconds since Jan 6, 1980. Minor time remains
in BCD format.
Note
: Bits 1, 2 and 3 of data A apply to Mode 4 GPS only (bc627AT).
Data B:
Bit 0: 0 = diagnostics on.
1 = diagnostics off <4>.
Bit 1: 0 = leap year off.
1 = leap year on.
Bit 2: 0 = enable jamsynchs.
1 = disable jamsynchs.
Bit 3: 0 = enable disciplining.
1 = disable disciplining.
<4>
Diagnostics feature deleted beginning with bc620/627AT Rev E hardware .
An example is provided in bc620.c. The example requires two hexadecimal digits to be entered
to cover the range of possible values 0 to 255.
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