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I/O Timing Characteristics#

This topic provides information about the camera's propagation delays ("response times") when operated via I/O lines.

The propagation delay is the length of time between the change of the analog I/O signal and the change of the camera's internal status – or vice versa.

Knowing the propagation delays is useful if you want to configure I/O control with a precision in the microsecond range.

All examples in this section assume that the Line Inverter feature is disabled.

Characteristics#

  • Propagation delays of opto-coupled I/O lines are generally longer than those of GPIO lines.
  • For opto-coupled input lines, the propagation delay for low-to-high signal transitions (rising edges) is shorter than for high-to-low signal transitions (falling edges). For GPIO lines, the opposite applies.
  • For output lines, the propagation delay for high-to-low signal transitions is always shorter.

Propagation Delays on Input Lines#

Input Line Propagation Delays

Propagation Delays on Output Lines#

Output Line Propagation Delays

Factors Influencing the Propagation Delays of I/O Lines#

Factor Opto-coupled Input Line GPIO Input Line Opto-coupled Output Line GPIO Output Line
Operating temperature ● ○ ● ○
Production spread of electronic components a ● ○ ● ○
Aging ● ●
External I/O supply voltage ● ● ○
Load resistance ● ○
Load current ● ○

● = major influence, ○ = minor influence

  1. Production spread can result in different propagation delays even in cameras from the same batch that are operated under identical conditions.

Recommendations#

  • As a general rule, use the fast edge of a signal to achieve the fastest response times. The propagation delays for a fast edge will rarely exceed 15 μs for an opto-coupled I/O line, and rarely 1 μs for a GPIO line.
  • To minimize fast edge propagation delays, increase the load resistance.
  • To minimize slow edge propagation delays:
    • Use an I/O supply voltage between 3.3 VDC and 5 VDC.
    • Decrease the load resistance to achieve a load current between 30 mA and 40 mA.
  • Use GPIO lines as their propagation delays are generally shorter.
  • Applying current to the input and output lines makes optocouplers age faster. Keep the times when current flows to a minimum to preserve stable propagation delays.
  • The signal edge-to-edge displacement (jitter) resulting from the use of I/O lines is negligible. However, the jitter may be increased by your trigger signal. To avoid jitter, keep the flanks of your trigger signals steep, and thereby short (preferably < 500 ns). The camera's inherent jitter is less than 100 ns, peak to peak.

Input Lines#

Fast Edge Slow Edge
Opto-coupled input line 4.5–7.5 μs (= rising edge) 19–28 μs (= falling edge)
GPIO input line <0.5 μs (= falling edge) <1 μs (= rising edge)

Output Lines#

Fast Edge Slow Edge
Opto-coupled output line 3–6 μs (= falling edge) 27–38 μs (= rising edge)
GPIO output line <0.5 μs (= falling edge) <2.5 μs (= rising edge)
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