Rainbow-electronics ATmega128RFA1 Manuel d'utilisateur Page 442

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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.
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