Document reference MAMPS-HW/E HARDWARE MANUAL
Edition 18 - March 2022 VM600 machinery protection system (MPS)
3-9
VM600 6U 19" rack backplane (ABE04x)
GENERAL SYSTEM DESCRIPTION
3.4.2 Tacho Bus
The Tacho Bus contains 8 parallel bus lines and is common to all slots in the ABE04x system
rack.
The Tacho Bus is primarily intended for the sharing of speed and phase reference signals
between various cards in the rack, such as between MPC4 / IOC4T card pairs and/or
XMx16 / XIO16T card pairs. Six Tacho Bus lines are available for speed/tacho signal sharing:
bus lines 1 to 6.
For example, speed signals can be put onto the Tacho Bus from an IOC4T card. This is done
by multiplexers that are under software control (see Figure 3-5). These multiplexers allow
one or both of the “local" speed signals on IOC #A to be sent to another card, for example to
IOC #B. Software-controlled demultiplexers on IOC #B allow the speed signal to be brought
off the bus and onto the card. Once on IOC #B, these signals can be used by the
corresponding MPC4 card (MPC #B). This technique is known as using “remote" speed
signals.
The Tacho Bus is also used for the routing of cold-junction compensation (CJC) signals
between AMC8 / IOC8T card pairs. Two Tacho Bus lines are reserved for CJC signal sharing:
bus lines 7 and 8.
NOTE: On the Tacho Bus, only the first six bus lines are available for speed/tacho signal
sharing (bus lines 1 to 6) as the last two bus lines are reserved for CJC signal
sharing (bus lines 7 and 8).
The VM600 MPSx software ensures that two or more speed signals are not sent to the same
Tacho Bus line. A signal on a given Tacho Bus line can be used by more than one card, for
example, by MPC4 / IOC4T card pairs and/or XMx16 / XIO16T card pairs.
NOTE: Refer to the relevant manual for further information: VM600 MPS1 software
manual or VM600 MPS2 software manual.
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