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Digitimer Ltd – D188 Operator's Manual

4:8 Digital Control

If eight digital outputs are not available, the operator can choose to use four digital outputs, defining a 4-

bit binary string that the D188 receives through pins 1 – 4 (D0 – D3). As with 1:1 mode, channels remain

active while the appropriate inputs are held TTL high.

Example Digital Input Configurations:

Channel 2 Active

Pin 1 = 0 (TTL low)

Pin 2 = 1 (TTL high)

Pin 3 = 0 (TTL low)

Pin 4 = 0 (TTL low)

Delay/De-bounce

The Delay/De-bounce setting allows the operator to introduce an adjustable delay in switching which can

be as long as 1000 milliseconds. This ensures that the voltage at any of the digital inputs has stabilised

before the D188 makes changes to the active electrode pair. This may be of use if mechanical switches

are used to control the D188, as "switch bounce" could be interpreted by the D188 as multiple rapid

changes between TTL low and high, rather than a single state change.

Minimum Switching Times & Stimulus Pulse Duration

It is important to appreciate that the electrode switching process is not instantaneous. It takes several

hundred microseconds for the D188 to switch channels in response to a change in the TTL state of the

digital inputs. We recommend that stimulus delivery and digital switching protocols are devised which

allow for a 1ms pause in stimulation following a digital input state change. If this pause is not adhered to,

stimulation may occur in multiple channels during the 1ms transition period.

The recommended 1ms pause, following changes in the digital inputs, is indicated by the red blocks in the

illustration above.

Channel 4 Active

Pin 1 = 0 (TTL low)

Pin 2 = 0 (TTL low)

Pin 3 = 1 (TTL high)

Pin 4 = 0 (TTL low)

Channel 5 Active

Pin 1 = 1 (TTL high)

Pin 2 = 0 (TTL low)

Pin 3 = 1 (TTL high)

Pin 4 = 0 (TTL low)

Version 1.2

Channel 8 Active

Pin 1 = 0 (TTL low)

Pin 2 = 0 (TTL low)

Pin 3 = 0 (TTL low)

Pin 4 = 1 (TTL high)