Details on M2i cards clock and trigger I/O section
(c) Spectrum GmbH
165
Details on M2i cards clock and trigger I/O section
The SMB clock and trigger I/O connectors of the M2i
cards from Spectrum are protected against over voltage
conditions.
For this purpose clamping diodes of the types 1N4148
are used. Both I/O lines are internally clamped to sig-
nal ground and to a specific clamping voltage named
Vt* for the trigger and Vc* for the clock line. So when
connecting sources with a higher level than the clamp-
ing voltage plus the forward voltage of typically
0.6..0.7 V will be the resulting maximum high-level lev-
el.
The maximum forward current limit for the used
1N4148 diodes is 100 mA.
When connecting a high performance clock or trigger
source with the card’s clock or trigger inputs, with logic
high levels above the clamping voltage please make
sure to not exceed the current limit of the clamping di-
odes.
This can most easily be ensured, when using the card’s
50 Ohm termination and a series resistor of 33 Ohm up
to 47 Ohm on the clock or trigger source.
To avoid floating levels with unconnected inputs, a pull
up resistor of 4.7 kOhm to 3,3V is used on each line.
The following table shows the values for the both clamp-
ing voltages Vt* and Vc*:
For details on how to read out the base hardware version from the driver or where to find that information on the cards type plate
please look up the relating sections in this manual.
Card series
Base Hardware Version
Vt*
Vc*
Trigger input 5.0 V tolerant
Clock input 5.0 V tolerant
M2i.xxxx
< V20
3.3 V
3.3 V
no
no
M2i.xxxx
> V20
5.0 V
3.3 V
yes
no
M2i.xxxx-exp
> V20
5.0 V
3.3 V
yes
no
