Owner's manual

© Sealevel Systems, Inc. - 11 -
DIO-16 User Manual
Relative Addressing vs. Absolute Addressing
The SeaIO API makes a distinction between “absolute” and “relative” addressing
modes. In absolute addressing mode, the Port argument to the API function acts as a
simple byte offset from the base I/O address of the device. For instance, Port #0
refers to the I/O address base + 0; Port #1 refers to the I/O address base + 1.
Relative addressing mode, on the other hand, refers to input and output ports in a
logical fashion. With a Port argument of 0 and an API function meant to output
data, the first (0
th
) output port on the device will be utilized. Likewise, with a Port
argument of 0 and an API function designed to input data, the first (0
th
) input port of
the device will be utilized.
In all addressing modes, port numbers are zero-indexed; that is, the first port is port
#0, the second port is #1, the third #2, and so on.
Direct Hardware Control
In systems where the user’s program has direct access to the hardware (i.e. DOS) the
table below gives the mapping and functions that the DIO-16 provides.
R = Read
R/W = Read or Write
Function Available Port Address Hex Port Type
RD A Base+0 Input Port (Opto Input)
B Base+1 Not Assigned
R/W C Base+2 Output Port (Reed Relays)
D Base+3 Not Assigned
RD = Read, RD/WR = Read or Write
Reading the Inputs
The inputs are active Low. If no voltage is applied across one of the differential
inputs it returns a one on that bit. If an AC or DC voltage is applied it returns a zero
on that bit.