OPTO 22 PCI-AC51, User Manual

Page: 28 / 48

PAMUX BUS RESET LINE
PCI-AC51 User’s Guide
24
Pamux Bus Reset Line
This section explains the terminology and functioning of the Pamux bus reset line and its interaction
between the PCI-AC51 card and the Pamux brains.
Purpose of the Reset Line
The purpose of the reset line on the Pamux bus is to provide a way to reset all the brains in the
system to their default power up state. Digital brains will turn OFF the digital output modules and
configure them as inputs. Analog brains will set all analog outputs to zero scale and configure them
as inputs.
See the Pamux User’s Guide (form 0726) for more details, including interaction with the watchdog
feature: http://www.opto22.com/documents/0726_Pamux_Manual.pdf
Reset Line Voltage
The pinout of the Pamux bus (50-pin ribbon cable) is listed in Chapter 4 (“Programming without the
Pamux driver”) of the Pamux Users Guide. The reset line is pin 49 of the ribbon cable. All
even-numbered pins are connected to logic ground. The state of the reset line can be verified by
measuring the voltage between pin 49 and any even pin.
Terminology
“LOW” and “HIGH”
The reset line is considered to be “LOW” when the voltage on the reset line is LOW (~ 0 VDC).
The reset line is considered to be “HIGH” when the voltage on the reset line is HIGH (~ 3.5 to 5.0
VDC).
Brain Reset Configuration: “Active HIGH” and “Active LOW”
Each Pamux brain has a jumper to configure whether the brain will reset when the reset line is HIGH
or LOW. This is referred to as reset “Active HIGH” or reset “Active LOW”.
If the brains are jumpered for reset “Active HIGH”, then the system will be “in reset” (the brains will be
reset) when the reset line is HIGH. The brains will function normally (not be reset) when the reset
line is LOW.
Similarly, if the brains are jumpered for reset “Active LOW”, then the system will be “in reset” (the
brains will be reset) when the reset line is LOW. The brains will function normally (not be reset) when
the reset line is HIGH.
You must determine whether you want your Pamux system to operate with reset Active HIGH or
reset Active LOW. Then consistently set the reset jumper on each brain in the system to match your
choice; all brains must use the same reset configuration. One consideration is how you want your
system to function if the computer loses power. Without power to the computer, the PCI-AC51
cannot drive the reset line high, so by default it will be low. You would want to analyze your system
needs to determine what is necessary for your system to automatically go into failsafe mode.