CHAPTER 3
INTERFACES
3.0 GENERAL
The TFP occupies 64 bytes in the VMEbus / VXlbus A16 address space. Refer to
SECTION 2.1
for
details on VMEbus base address selection, and to
SECTION 2.2
for VXlbus Logical Address
selection. TFP data transfers are D16 with the exception of packet I/0 which allows D08(0)
transfers. A glossary of key terms commonly used in the discussion of timing operation is provided
below.
EPOCH
A reference time or event. Epoch often refers to a one pulse per second event.
FLYWHEEL
To maintain time or frequency accuracy as well as local resources allow when a time or frequency
reference has been lost or removed.
PERIODIC
A programmable frequency which is obtained by dividing the TFP reference frequency. Periodics
are sometimes referred to as 'heartbeats'. Periodics may optionally be synchronous with the 1PPS
epoch if the period is expressible as a ratio of integers.
MAJOR TIME
Units of time larger than or equal to seconds. A
day hr:min:sec
format is usually implied.
MINOR TIME
Subsecond time to whatever resolution is supported.
PACKET
A group of bytes conforming to a defined structure. Packets are usually used in bit serial or byte
serial data transmission to allow framing of the transmitted data.
3.1 DATA INPUT AND OUTPUT
Communication with the TFP is performed using a set of memory mapped registers. These registers
may be read only (R), write only (W), or read/write (R/149. In some cases a read/write register is
structured to support dissimilar data in the
read
and
write
directions. The table below summarizes
the type of register located at each hexadecimal offset, and provides a brief description of the register
function. The data format and detailed descriptions of each register are provided in the next section.
Datum Inc., Bancomm Div.
bc635VME/bc350VXI Manual
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