For reference, here is a Japanese manual with information on the JVS protocol:
http://superusr.free.fr/arcade/JVS/JVST_VER3.pdf
I was following its diagrams for the USB Type B port, but I believe they have the diagram incorrect for the location of Pin 1 and 2.
At any rate, with some bad translation, I can get some information about the Sense line:
Control and address allocation of the terminator by SENSE line
sense line is 0V, 2.5V (2~3V), to define the three voltage of 5V. 5V guess is ahead of I / O board
It shows that no (this time terminator is ON), 2.5V the previous I / O board address setting other than
It indicates the previous state, 0 V indicates that the preceding I / O board is completed address setting. Address of the set
See Attachment 3 for instructions. (Sense input side to pull up to 5V).
Even sense output is not power is supplied, do not become 0 V (drawn current to GND
Absent). In the case of the middle of the I / O power supply OFF, it can detect power outage on the main board.
SENSE output circuit example
Even in the state of each node (I / O board) is the power OFF, be in the circuit, such as not to catch a sense line to GND
Rukoto (*not sure what this is...).
Here's a translated diagram of the output:
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zaFVbU+QMXioo6/w9pI4s6gUK7woq6QOCqijr/D2kjizqBQjv/I6z9/bvMizp/4EJdUecvz/w/A38+YAeBdqPRSP7EbduWnsGB+RlGFDhDTrbwFt/KD//NCiH8ZzoF3kINAu2IzYO0IxRA2hEKIO0IBZB2hAJIO0IBpB2hANKOUABpRyiAtCMUQNoRCiDtCAWQdoQC/g+mEiqIRT7CLgAAAABJRU5ErkJggg==
I take this all to mean that I should be outputting 2.5v rather than 5v. I think the MEGA has 5v TTL whereas the Teensy might be 3.3v and, in the case of the TeensyJVS project, wouldn't need the voltage divider...
So... this leads me to believe I've got 2 things going on:
1. My voltage measurement on the stock hardware might have been off?
2. I likely need to incorporate a voltage divider into my output, per the diagram, and try again with my emulator hardware.
Scratch that... If I'm reading that diagram correctly, the Output of the IO board is simply driving a transistor that sinks the Sense line to ground. I don't think I have to mess with a voltage divider or worry about my TTL level.