libftdi Archives

Subject: Unexpected feature aka BUG in FT2232 Chips

From: Uwe Bonnes <bon@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
To: libftdi@xxxxxxxxxxxxxxxxxxxxxxx
Date: Tue, 29 Sep 2009 19:54:12 +0200
Hallo,

the FT2232 MPSSE commands
3.5.1 Clock Data to TMS pin (no read) 0x4A or 0x4B
and probably 
3.5.2 Clock Data to TMS pin with read 0x6A or 0x6B or 0x6E or 0x6F

have an undocumented feature or bug when sending 7 bits of TMS data. This
data is in bit 0-6 of the Byte1 argument, while Bit 7 is the TDO value
constantly applied to TDI/DO. Observations show, that this TDO value is also
applied to TMS on the second edge of 7'th TCK. leading to unexpected
behaviour.

Bye
-- 
Uwe Bonnes                bon@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

Institut fuer Kernphysik  Schlossgartenstrasse 9  64289 Darmstadt
--------- Tel. 06151 162516 -------- Fax. 06151 164321 ----------

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