Understanding the interface in Hitec HMI

Hitec robotics including ROBONOVA humanoid, HSR-8498HB servos, MR C-3024 Controllers and RoboBasic
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Understanding the interface in Hitec HMI

Post by kiendaica » Thu Apr 14, 2011 1:13 pm

Post by kiendaica
Thu Apr 14, 2011 1:13 pm

I'm building a robot using hitec servos and I found the article by Richard Ibbotson
Hitec HSR-8498HB Digital Servo Operation and Interface
http://robosavvy.com/Builders/i-Bot/HSR8498HB%20Servo.pdf

I just try to understand how the circuit work in page 7, (the Hitec HMI schematic)
Basically, if the servo sending out logic '1', the voltage at the gate of transistor Q2 will be approximately Vbat, the gate is in 'ON' state, and current will flow from drain to source in Q2, making Tx = '0'.
If the servo sending out logic '0', Q2 gate is in 'OFF' state, and the voltage at Tx will be Vbat, hence Tx= '1'.

If Rx='0', Q1 gate is in 'OFF' state, the servo will receive logic '1'
If Rx='1', Q1 gate is in 'ON' state, and current will flow from drain to source in Q1, and hence the servo will receive logic '0'.

Therefore, this circuit acts as an inverter and combining the transmit and receive signal in the same wire going to the servo.

Could anyone please verify whether my explanation is correct?
In addition, when the servo is sending '1' and receiving '0' (when Rx='1'), isn't there a conflict? I guest that in this half-duplex serial communication, the protocol disallow sending and receiving at the same time?

Any comment would be greatly appreciate! :D
I'm building a robot using hitec servos and I found the article by Richard Ibbotson
Hitec HSR-8498HB Digital Servo Operation and Interface
http://robosavvy.com/Builders/i-Bot/HSR8498HB%20Servo.pdf

I just try to understand how the circuit work in page 7, (the Hitec HMI schematic)
Basically, if the servo sending out logic '1', the voltage at the gate of transistor Q2 will be approximately Vbat, the gate is in 'ON' state, and current will flow from drain to source in Q2, making Tx = '0'.
If the servo sending out logic '0', Q2 gate is in 'OFF' state, and the voltage at Tx will be Vbat, hence Tx= '1'.

If Rx='0', Q1 gate is in 'OFF' state, the servo will receive logic '1'
If Rx='1', Q1 gate is in 'ON' state, and current will flow from drain to source in Q1, and hence the servo will receive logic '0'.

Therefore, this circuit acts as an inverter and combining the transmit and receive signal in the same wire going to the servo.

Could anyone please verify whether my explanation is correct?
In addition, when the servo is sending '1' and receiving '0' (when Rx='1'), isn't there a conflict? I guest that in this half-duplex serial communication, the protocol disallow sending and receiving at the same time?

Any comment would be greatly appreciate! :D
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