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Topic: BB3 KT-link buffer logic design question (Read 122 times) previous topic - next topic

BB3 KT-link buffer logic design question

Hello,

looking at schematic of KT-link buffer logic (implemented by CPLD) I came across question of ADBUS2 (FT_TDO) pin configuration. It seems this pin is always driven to '1' or '0' by the multiplexer output - it is never 'high Z'. In case the BBv3 is not connected to target, ADBUS2 ((FT_TDO) is driven to high or low randomly, due to the fact that input 'TDO' is floating; not pulled up. However, before the OpenOCD is started, both channels of the FT2232H are configured as UART, with ADBUS2 being configured as RTS# output -> driven high. That means that in case BBv3 (in KT-link configuration) is powered (connected to USB), but disconnected from the target, there is a real danger of damaging FT2232H or CPLD, because their pins (both of which are in the role of outputs) are connected, possibly driven to opposite rails. Is my reasoning correct ?

Edit: I fixed a typo,