Rainbow Electronics ATmega128RFA1 - Manual (Page 442)

442
8266A-MCU Wireless-12/09
ATmega128RFA1
• Reset Register
• Boundary-scan Chain
29.3.1 Bypass Register
The Bypass Register consists of a single Shift Register stage. When the Bypass
Register is selected as path between TDI and TDO, the register is reset to 0 when
leaving the Capture-DR controller state. The Bypass Register can be used to shorten
the scan chain on a system when the other devices are to be tested.
29.3.2 Device Identification Register
Figure 29-1. The Format of the Device Identification Register
MSB LSB
Bit 31 28 27 12 11 1 0
Device ID Version Part Number Manufacturer ID 1
4 bits 16 bits 11 bits 1 bit
29.3.2.1 Version
Version is a 4-bit number identifying the revision of the component. The JTAG version
number follows the revision of the device. Revision A is 0x0, revision B is 0x1 and so
on.
29.3.2.2 Part Number
The part number is a 16-bit code identifying the component. The JTAG Part Number for
ATmega128RFA1
is listed in Table 31-6 on page 467 .
29.3.2.3 Manufacturer ID
The Manufacturer ID is a 11-bit code identifying the manufacturer. The JTAG
manufacturer ID for ATMEL is listed in
Table 31-6 on page 467 .
29.3.3 Reset Register
The Reset Register is a test Data Register used to reset the part. Since the AVR tri-
states Port Pins when reset, the Reset Register can also replace the function of the
unimplemented optional JTAG instruction HIGHZ.
A high value in the Reset Register corresponds to pulling the external Reset low. The
part is reset as long as there is a high value present in the Reset Register. Depending
on the fuse settings for the clock options, the part will remain reset for a reset time-out
period (see
"Clock Sources" on page 148 ) after releasing the Reset Register. The
output from this Data Register is not latched, so the reset will take place immediately,
as shown in
Figure 29-2 on page 443 .