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Single ended encoder signal to Brick Controller


wlewis
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I wish to connect a single-ended encoder signal to a Brick Controller. Documentation in the Turbo PMAC User Manual (p 49) suggests that single-ended encoder signals are acceptable, but the Brick Controller HRM (p9) says that only differential quadrature signals can be used.

 

Can you please clarify whether the Brick Controller can accept a single-ended encoder signal?

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Thanks Sina.

 

I've done this, but I'm still not seeing the encoder counts at all. The signalling level from the encoder is LVTTL, and I'm seeing approximately 3.2 V amplitude on the square wave from the encoder when I look at it on a scope.

 

Is this likely to work, or do I need to add some circuitry to bring the voltage up to 5 V?

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wlewis,

 

In Brick family of products we use ST34C86 QUAD RS-422, RS-423 CMOS differential line receivers on encoder inputs. An LVTTL can drive an original TTL because the output voltage specification of an LVTTL is within the TTL range. The LVCMOS also can drive a TTL and LVTTL. However, the output voltage specification of a LVTTL is not compatible with input specification of a CMOS, it may work for some design, and not for some other, or even work some day, to stop working on other days.

 

CMOS have more strict requirement, where TTL is more relaxed. Originally, genuine TTL were more robust to signal degradations than CMOS, because of the more relaxed input requirement.

 

Since we are using differential line receivers, the input hysteresis is about 60 mV on differential input lines. Since you have a single ended encoder with an output of 3.2V and we are pulling the complementary lines to 2.5V, we are well over 60 mV input difference and you should be able to see the inputs, if both encoder and Brick are on the same ground. Please make sure that the encoder ground is connected to pin 12 (GND) of encoder input connector.

 

Also, if you can bring up the signal voltage to 5V, you should be able to read your encoder.

 

Regards,

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