Frequently Asked Questions
Q. My hwvers register is showing all zero's. Which version is my board?
PCB/HW version recognition is a new hardware feature in v4.0 boards. If
your hwvers register field is showing all zeros, it means your board is
version 3 or earlier.
In effect this means that your board cannot handle frequencies higher
than 4.16kHz and only outputs pulses 1.2us wide.
Q: What are the on-board switches for?
Switch | Description |
---|---|
SW1.1 | Glitch filter enable (see Section 3 of the user guide) |
ON - glitch fillter enabled, output jitter present | |
OFF - glitch filter disabled, no output jitter (default) | |
SW1.2 | Input termination enable (see Section 2.3 of the user guide) |
ON - input terminations for all channels are turned on | |
OFF - input terminations for all channels are turned off) | |
SW1.3 | Output termination enable (see Section 2.3 of the user guide) |
ON { output terminations for all channels are turned on | |
OFF { output terminations for all channels are turned off | |
SW2.4 | TTL/TTL-BAR selection switch (see Section 4.2 of the user guide) |
ON { TTL channels receive and generate TTL (default) | |
OFF { TTL channels receive and generate TTL-BAR |
General-purpose switches not listed in the table perform no particular function, but their setting is reflected in the status register
Multicast switchesare implemented, and can be used to select a
multicast address for the board. At the moment, no particular
functionality is defined
in this respect, but setting a switch to ON is reflected in the other
switches
register (OSWR)
Q: Are the input and output lines terminated?
Each input and output channel has a selectable 100 Ohms termination,
which can be enabled by the
input and output termination switches ( see Section 3 of the user
guide on on-board switches).
Q: How many nodes can one RS485 output drive?
Each RS485 output on a channel has its dedicated transceiver capable of driving 256 nodes
Q: How many channels does a TTL to RS485 pulse converter system have?
- With CONV-TTL-RS485 motherboard only. Six pulse conversion channels. Each channel has one TTL/TTL-BAR input and one TTL/TTL-BAR output.
-
TTL to TTL
-
TTL-BAR to TTL-BAR
- CONV-TTL-RS485 motherboard with CONV-TTL-RS485-RTM-DB9 board. Two pulse conversion channels in RS485. Each channel has one TTL/TTL-BAR output and five RS485 outputs.
-
TTL to RS-485
-
TTL-BAR to RS-485
-
RS-485 to TTL
-
RS-485 to TTL-BAR
-
RS-485 to RS-485
- CONV-TTL-RS485 motherboard with CONV-TTL-RS485-RTM-OPT board. Three pulse conversion channels in Optical. Each channel has one TTL/TTL-BAR output and two optical outputs.
-
TTL to Optical
-
TTL-BAR to Optical
-
Optical to TTL
-
Optical to TTL-BAR
-
Optical to Optical
Additionally, you also have four general-purpose inverter channels on the front panel. These can be used to invert a signals locally, without having to remove the board from the rack.
As an example, if your TTL switch is set to TTL signals and you need to repeat/convert a TTL-BAR signal, you don't need to remove the board from the rack, flip a switch and plug it back. You can use one of the INV-TTL channels to reverse the polarity of the TTL-BAR signal and use it to your will. Bear in mind that if you want to repeat this TTL-BAR signal, you need to use another INV-TTL channel to reverse the polarity the CONV-TTL-RS485 is outputting, since the CONV-TTL-RS485 will output TTL signals.
Q: How do I know if an RTM is correctly connected to the rear for the VME backplane?
There is a memory register that signals if an RTM is connected and what
type it is. For conv-ttl-rs485 boards, the RTM lines indicated the type
of RTM connected.
Other RTM information will apply to other types of RTMs such as the ones
that plug into the sister-board
conv-ttl-blo.
Have a look at the description of RTM detection
lines
to find out more about your RTM.
Q: Can I obtain more than five RS485 signals out of a single one?
When using the CONV-TTL-RTM-RS485-RTM-DB9, two RS485 channels are
available, each with 5 outputs.
You can form a daisy-chain on the front panel using the TTL channels,
and use the RS485 outputs of each channel to repeat your signal. Like
this, you can repeat one RS485 signal into a maximum of 10. Keep in mind
there is a delay associated with each channel.
Q: Can I uses LVTTL input levels?
Yes, the TTL input is made of a parallel 50 Ohm termination and a SN74LVC14AD Schmitt trigger inverter. The inputs are compatible to TTL and LVTTL input levels.
Q: What to do to have a low jitter?
When needing a low jitter on the output signal, just make sure that SW1.1 is set in the position OFF (User Guide, pages 16 and 26-27). With this (default) setting the signal chain is fully combinatorial. The jitter is then virtually 0, and negligible compared to the RS485 level signal rise time
Denia Bouhired, January 9th, 2018