Rainbow Electronics ATmega162V - Manual (Page 313)

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ATmega162/V
2513E–AVR–09/03
Erratas
The revision letter in this section refers to the revision of the ATmega162 device.
ATmega162, all rev. There are no errata for this revision of ATmega162. However, a proposal for solving
problems regarding the JTAG instruction IDCODE is presented below.
IDCODE masks data from TDI input
The public but optional JTAG instruction IDCODE is not implemented correctly
according to IEEE1149.1; a logic one is scanned into the shift register instead of the
TDI input while shifting the Device ID Register. Hence, captured data from the pre-
ceding devices in the boundary scan chain are lost and replaced by all-ones, and
data to succeeding devices are replaced by all-ones during Update-DR.
If ATmega162 is the only device in the scan chain, the problem is not visible.
Problem Fix/ Workaround
Select the Device ID Register of the ATmega162 (Either by issuing the IDCODE
instruction or by entering the Test-Logic-Reset state of the TAP controller) to read
out the contents of its Device ID Register and possibly data from succeeding
devices of the scan chain. Note that data to succeeding devices cannot be entered
during this scan, but data to preceding devices can. Issue the BYPASS instruction
to the ATmega162 to select its Bypass Register while reading the Device ID Regis-
ters of preceding devices of the boundary scan chain. Never read data from
succeeding devices in the boundary scan chain or upload data to the succeeding
devices while the Device ID Register is selected for the ATmega162. Note that the
IDCODE instruction is the default instruction selected by the Test-Logic-Reset state
of the TAP-controller.
Alternative Problem Fix/ Workaround
If the Device IDs of all devices in the boundary scan chain must be captured simul-
taneously (for instance if blind interrogation is used), the boundary scan chain can
be connected in such way that the ATmega162 is the fist device in the chain.
Update-DR will still not work for the succeeding devices in the boundary scan chain
as long as IDCODE is present in the JTAG Instruction Register, but the Device ID
registered cannot be uploaded in any case.