ADLINK PCI-7442 - Manual (Page 53)

Register Format 41
The isolated DO statuses can be read back from the registers.
When you want to read the 64-bit DO statuses, you must first send
the Read Back Start command (BASE+0x80h). You can in turn
read the isolated DO when DO read back procedure is ready.
DO ReadBack Start does not need any register value. You only
need to send out the address (BASE + 0x80h) in Read mode
before reading back all 64-bit channel output data. When the
back2 receives the Start command, the 64-bit DO data readback
procedure proceeds. You can check if the DO readback procedure
is finished by get nDO_RBReady flag status.
Address R/W Value Mapping (MSB----LSB)
BASE+0x80h R DO Read Back Start
BASE+0x82h R IDO[15…0]
BASE+0x84h R IDO[31...16]
BASE+0x86h R IDO[47...32]
BASE+0x88h R IDO[63...48]
Bit value: 0: Output Power MOSFET is OFF. (Initial value)
1: Output Power MOSFET is ON.