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GR716-DS-UM, May 2019, Version 1.29
348
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GR716
the status register to go low. An output pulse is also produced when conditions for external datation is
met. The pulse is driven for one system clock period on the occurrence of external save condition.
If a simpler version of latching the time is needed based on a signal going high at any instance then
the latch and save signals can be provided with the same input.
There are four External datation services implemented and each of them has its own mask EDMx, sta-
tus EDS and time EDxETx registers. All the four External datation services are based on the input
latch and save signal vectors. The external datation pulse vector consist of four outputs corresponding
to each of the external datation services.
34.4
Data formats
All Elapsed Time (ET) information is compliant with the CCSDS Unsegmented Code defined in
[CCSDS] and repeated hereafter.
34.4.1 Numbering and naming conventions
Convention according to the CCSDS recommendations, applying to time structures:
•
The most significant bit of an array is located to the left, carrying index number zero.
•
An octet comprises eight bits.
Table 438.
CCSDS n-bit field definition
Convention according to AMBA specification:
•
The least significant bit of an array is located to the right, carrying index number zero.
•
Big-endian support.
Table 439.
AMBA n-bit field definition
34.5
Reference documents
[CCSDS] Time Code Formats, CCSDS 301.0-B-4, www.CCSDS.org
[SPW]
Space engineering: SpaceWire - Links, nodes, routers and networks, ECSS-E-ST-50-12C
[RMAP] Space engineering: SpaceWire - Remote memory access protocol, ECSS-E-ST-50-52C
CCSDS n-bit field
most significant
least significant
0
1 to n-2
n-1
AMBA n-bit field
most significant
least significant
n-1
n-2 down to 1
0