ARM-USB-OCD-H small amplitude of the TTCK and other signals

Started by Ievgen, December 07, 2018, 11:21:42 AM

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Hi I use ARM-USB-OCD-H with Cypress FX3 device. I have installed drivers from OpenOCD 4.0 for ARM-USB-OCD-H and installed OpenOCD 6.0 as specified at Cypress documentation.

When I try to connect ARM-USB-OCD-H using OpenOCD I have problem - debuger not connected.
My devboard have independent power supply. I use only:

TTRST_N - 3 pin
TTDI    - 5 pin
TTMS    - 7 pin
TTCK    - 9 pin
TTDO    - 13 pin
and GND pins of the 20 pins JTAG connector

I see using oscilloscope that TTCK level (and other signals level) down from 1500 mV to <500 mV.

It seems like output stage power shutdown in the ARM-USB-OCD-H.

Please help me to fix it!


What is the voltage of the target? I feel like you would need to connect pin #1 VREF to the target's supply, else JTAG signals would be at 3.3V per default and you might experience problems with signal's levels. Especially if the target's voltage is lower than 2.0V.
Technical support and documentation manager at Olimex


Thank you, problem was fixed!

ARM-USB-OCD-H, ARM-USB-OCD User`s Manual have only information: Pins 1 and 2 of the JTAG connector are voltage reference that probes if the target is already
powered by another source. If it is not, the ARM-USB-OCD would attempt to power it by 5V at pin
19 of the connector.

And no information about output stage to understand how it work.


Yes, this is half of the information. For ARM-USB-OCD and ARM-USB-OCD-H, VREF is also used to adjust the levels of all JTAG signals near the targets voltage.
Technical support and documentation manager at Olimex