atmega3250v-8auatmega325v-8ai ATMEL Corporation, atmega3250v-8auatmega325v-8ai Datasheet - Page 286

• Manufacturer Part Number: atmega3250v-8auatmega325v-8ai
• Description: Atmega3250 8-bit Microcontroller With In-system Programmable Flash
• Manufacturer: ATMEL Corporation

27.8.7
27.8.8
27.8.9
27.8.10
286
ATmega325/3250/645/6450
Data Registers
Reset Register
Programming Enable Register
Programming Command Register
The Data Registers are selected by the JTAG instruction registers described in section
gramming Specific JTAG Instructions” on page
programming operations are:
•
•
•
•
The Reset Register is a Test Data Register used to reset the part during programming. It is
required to reset the part before entering Programming mode.
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 (refer to
Sources” on page
not latched, so the reset will take place immediately, as shown in
The Programming Enable Register is a 16-bit register. The contents of this register is compared
to the programming enable signature, binary code 0b1010_0011_0111_0000. When the con-
tents of the register is equal to the programming enable signature, programming via the JTAG
port is enabled. The register is reset to 0 on Power-on Reset, and should always be reset when
leaving Programming mode.
Figure 3. Programming Enable Register
The Programming Command Register is a 15-bit register. This register is used to serially shift in
programming commands, and to serially shift out the result of the previous command, if any. The
JTAG Programming Instruction Set is shown in
in the programming commands is illustrated in
Reset Register
Programming Enable Register
Programming Command Register
Flash Data Byte Register
26) after releasing the Reset Register. The output from this Data Register is
TDO
TDI
D
A
T
A
0xA370
=
ClockDR & PROG_ENABLE
Figure
Table
D
Q
27-15.
284. The Data Registers relevant for
27-16. The state sequence when shifting
Programming Enable
Figure 25-2 on page
2570L–AVR–08/07
225.
“Clock
“Pro-