I/O Timing Characteristics#
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.
- 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#
Propagation Delays on Output Lines#
Factors Influencing the Propagation Delays of I/O Lines#
|Factor||Opto-coupled Input Line||GPIO Input Line||Opto-coupled Output Line||GPIO Output Line|
|Production spread of electronic components a||●||○||●||○|
|External I/O supply voltage||●||●||○|
● = major influence, ○ = minor influence
Production spread can result in different propagation delays even in cameras from the same batch that are operated under identical conditions.
- 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 opto-couplers 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 below 500 ns). The camera's inherent jitter is less than 100 ns, peak to peak.
Propagation Delays Measured on ace USB 3.0 Cameras#
The propagation delays measured are based on 2000 ace USB 3.0 cameras from the same production batch.
The values in the following tables are only valid under the following operating conditions:
- Housing temperature: 25 °C
- Load resistance: 170 Ω
- I/O supply voltage: 5 VDC
Don't base assumptions about propagation delays under different operating conditions on these values.
|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)|
|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)|