ccTalk Paylink Lite 2 User Manual
Aardvark Embedded Solutions Ltd.
Issue 1.1
3
rd
August 2018
Page 11
4
USB Reset and LED Operation
4.1 USB Reset Strategy
Each variant of the Paylink Lite 2 family is fitted with a very simple
microcontroller.
The primary purpose of this microcontroller is to manage the USB connection
to the PC.
PC USB circuitry is “fragile” and the connection of physical peripherals
through a USB link can induce noise within the PC. This noise can cause the
PC operating system to “hang”.
The approach that Paylink Lite 2 takes is to detect failures in the USB
communications system. On detecting these failures, the Paylink Lite 2
automatically disconnects itself from the USB bus and reconnects itself a
short time later.
This technique, effectively resetting the USB, has shown itself to be very
effective in fixing any USB link hanging.
At start of world, there is a five-minute period where the microcontroller does
not check for regular activity. If regular activity is detected, then no reset is
applied to the FTDI device.
After that period, if no activity is detected, then the microcontroller enters a
cycle of four timing patterns, with "off" and "on" timings as follows:
1. 5 seconds Off
30 seconds On
2. 10 seconds Off
60 seconds On
3. 15 seconds Off
90 seconds On
4. 20 seconds Off
120 seconds On
Whenever the microcontroller gets to the fourth ti
ming pattern, it “sticks” there
until activity is detected.
