Rainbow Electronics Atmega169L - Manual (Page 226)

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ATmega169V/L
2514A–AVR–08/02
The IEEE std. 1149.1 also specifies an optional TAP signal; TRST – Test ReSeT –
which is not provided.
When the JTAGEN Fuse is unprogrammed, these four TAP pins are normal port pins,
and the TAP controller is in reset. When programmed, the input TAP signals are inter-
nally pulled high and the JTAG is enabled for Boundary-scan and programming. The
device is shipped with this fuse programmed.
For the On-chip Debug system, in addition to the JTAG interface pins, the RESET pin is
monitored by the debugger to be able to detect external reset sources. The debugger
can also pull the RESET pin low to reset the whole system, assuming only open collec-
tors on the reset line are used in the application.
Figure 104. Block Diagram
TAP
CONTROLLER
TDI
TDO
TCK
TMS
FLASH
MEMORY
AVR CPU
DIGITAL
PERIPHERAL
UNITS
JTAG / AVR CORE
COMMUNICATION
INTERFACE
BREAKPOINT
UNIT
FLOW CONTROL
UNIT
OCD STATUS
AND CONTROL
INTERNAL
SCAN
CHAIN
M
U
X
INSTRUCTION
REGISTER
ID
REGISTER
BYPASS
REGISTER
JTAG PROGRAMMING
INTERFACE
PC
Instruction
Address
Data
BREAKPOINT
SCAN CHAIN
ADDRESS
DECODER
ANALOG
PERIPHERIAL
UNITS
I/O PORT 0
I/O PORT n
BOUNDARY SCAN CHAIN
Analog inputs
Control & Clock lines
DEVICE BOUNDARY