I/O Timing Characteristics (ace, ace 2, boost)
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

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 |
Operating temperature |
● |
○ |
● |
○ |
Production spread of electronic componentsa |
● |
○ |
● |
○ |
Aging |
● |
|
● |
|
External I/O supply voltage |
● |
|
● |
○ |
Load resistance |
|
|
● |
○ |
Load current |
|
|
● |
○ |
● = major influence, ○ = minor influence
a 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.
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 should also apply to ace 2 cameras.
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.
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
(ace classic/U/L only) |
3–6 μs (= falling edge) |
27–38 μs (= rising edge) |
GPIO output line |
<0.5 μs (= falling edge) |
<2.5 μs (= rising edge) |