Sensoray 621 - Manual (Page 8)

Sensoray Model 621/721 Instruction Manual Page 6
5.2.1 I/O Ports
Reading an I/O port returns either the input logic level (input mode) or the state of the output register
(output mode).
The DDR registers are used to set a particular I/O group to function as either inputs or outputs. The
DDR bits affect the I/O channels as shown in the table below.
DDR9 DDR8 DDR7 DDR6 DDR5 DDR4 DDR3 DDR2 DDR1 DDR0
CHANNELS
68-71
CHANNELS
64-67
CHANNELS
56-63
CHANNELS
48-55
CHANNELS
40-47
CHANNELS
32-39
CHANNELS
24-31
CHANNELS
16-23
CHANNELS
8-15
CHANNELS
0-7
If a DDR bit is set to zero the associated channels will be inputs. When a DDR bit is set to one the
associated channels will be outputs.
A channel’s output register will be immediately output when a channel is first configured as an output.
To avoid unwanted output levels when configuring DIOs as outputs, preset the output registers (write to
the associated channels) with desired values before configuring as outputs.
Note: The values read and written to the I/O ports are true (i.e. not inverted).
5.2.2 Latch/Output Enable Mode
Latching and Output Enable is available on channels 64-71.
When the LOE bit (bit 17) of the “ Data direction/Misc./Status” register is set to one, LOE mode is in
effect. In this mode, data present on input channels 64-71 is latched into a holding register when the
LATCH input signal is asserted low. The host may read latched data at any time. Additionally, output
channels are tri-stated while the OUTEN input signal is asserted high.
Note: Channels 64-71 behave as standard DIOs when LOE is not set to one.
The light emitting diode ‘D1’ is linked to the LOE bit of the “ Data direction/Misc./Status” register. The
LED is on when LOE is set to zero, and off when LOE is set to one.
5.2.3 Edge Type Select Register (channels 0-63)
Input channels may be configured to detect either rising or falling edge transitions. Set the bits in the
“edge select” to “0” to detect rising edges for the associated relay channels, or to “1” to detect falling edges.
5.2.4 Arming & Disarming Capture (channels 0-63)