Picobus - further information
This page expands on our basic picobus information page.
There is one dual function line, Q3-, which can function as a switch to Vcc
and/or as a negative supply, depending on the microprocessor
motherboard implementation. No system has yet implemented this feature,
however the circuit excerpt shown has been prototyped and tested.
The presence of a negative voltage simplifies the design of
some circuitry. The -7V may also be used in conjunction
with the +5V to supply 12V for a relay coil. The translation of
a normal Qn signal, which is typically 0v...5v level, to the Q3-
signal, which is -7v...5v level, does require extra circuitry.
A typical circuit for this translation appears below.
No negative supply
Q3- function same as Q0-Q2
No Q3 Mux select
Q3- is nominal -7V
Both -Vee and Q3 Muxsel
Q3- is push-pull driver, switch to Vcc at time T=3, switch to -7V at other times
Note: This circuit is presented as a typical
example only and is not mandatory
|Implementing optional Q3-|
utilizing the -7V rail must include a supply switch, such that
-7V is only connected when +5V and Gnd are detected.
Devices using -7V should also feature a prominent warning
in the instructions for the user to remove power before
connecting or disconnecting the Picobus connector.
This page had a Maintenance update: 23 April 2013