SIS Documentation
SIS3820
VME Scaler
Page 62 of 79
12.4 TTL
The TTL input level option is possible with LEMO and flat cable connectors.
12.4.1 High impedance TTL/LEMO
The (low active) TTL/LEMO input circuitry is sketched below. 1 K
Ω
and 4,7 K
Ω
termination
are available as options. A high active version can be implemented by replacing the 74F245
with a 74F640
12.4.2 50
Ω
TTL/LEMO
The (high active) TTL/LEMO 50
Ω
input impedance circuitry is shown below.
12.4.3 TTL/Flat Cable
In the flat cable TTL version the positive (right hand side) of the connector is tied to ground.