74
AT94KAL Series FPSLIC
Rev. 1138G–FPSLI–11/03
undetermined state when exiting the test mode. If needed, the BYPASS instruction can be
issued to make the shortest possible scan chain through the device. The AVR can be set in
the reset state either by pulling the external AVR RESET pin Low, or issuing the AVR_RESET
instruction with appropriate setting of the Reset Data Register.
The EXTEST instruction is used for sampling external pins and loading output pins with data.
The data from the output latch will be driven out on the pins as soon as the EXTEST instruc-
tion is loaded into the JTAG IR-register. Therefore, the SAMPLE/PRELOAD should also be
used for setting initial values to the scan ring, to avoid damaging the board when issuing the
EXTEST instruction for the first time. SAMPLE/PRELOAD can also be used for taking a snap-
shot of the AVR’s external pins during normal operation of the part.
The JTAG Enable bit must be programmed and the JTD bit in the I/O register MCUR must be
cleared to enable the JTAG Test Access Port.
When using the JTAG interface for Boundary-Scan, using a JTAG TCK clock frequency higher
than the internal chip frequency is possible. The chip clock is not required to run.
Data Registers
The Data Registers are selected by the JTAG instruction registers described in section
“Boundary-scan Specific JTAG Instructions” on page 75. The data registers relevant for
Boundary-Scan operations are:
•
Bypass Register
•
Device Identification Register
•
AVR Reset Register
•
AVR Boundary-Scan Chain
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.
Device
Identification
Register
Figure 41 shows the structure of the Device Identification register.
Figure 41.
The format of the Device Identification Register
Version
Version is a 4-bit number identifying the revision of the component. The relevant version num-
bers are shown in Table 18.
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
Table 18.
JTAG Part Version
Device
Version (Binary Digits)
AT94K05
–
AT94K10
0010
AT94K40
–