HW modification for jitter-free calibration frequency out

[Ho-Ro]

The calibration output is generated by toggling an output pin in an interrupt routine triggered by counter/timer 2 overflow. Due to interrupt latency the signal jitters by some µs, this leads to a high phase jitter on high output frequencies. The EzUSB can provide the T2 overflow signal on pin PE2/T2OUT as an alternate port function (PE2 is available on JP2 of the PCB, at least for 6022BE, for 6022BL you must solder directly on pin 88 of the 100-pin TQFP EzUSB chip). According to TRM (rev. G, p.193) the signal is "one CLKOUT pulse". Add a D-flipflop (e.g. 74HC74) to create the correct frequency with a 50% duty cycle.

Depending on your needs, supply the flipflop either with 5V (pin 3 of U5 - AMS1117-3.3) or with 3.3V (pin 2 of U5), GND is U5/pin1.
More info in the FW discussion #16.
This FW mod works perfectly with my 6022BE and is available in Openhantek for 6022BE and BL since commit 5973a32.

[cryptozoy]

Binary counters like 74HC161 or 74HC163 can be used here too. Install what you have. ;-)

[Ho-Ro]

Install what you have. ;-)

I did, in my scope works a 74HC4024 (7-bit ripple counter, Q0 used), the 1st DIL counter I found in my junk box.