Rainbow-electronics ATmega64L Manual do Utilizador descarregar pdf (Página 226)

226

ATmega16(L)

2466B–09/01

Figure 118. Additional Scan Signal for the Two-wire Interface

Scanning the RESET Pin The RESET pin accepts 5V active low logic for standard reset operation, and 12V active

high logic for High Voltage Parallel programming. An observe-only cell as shown in Fig-

ure 119 is inserted both for the 5V reset signal; RSTT, and the 12V reset signal;

RSTHV.

Figure 119. Observe-only Cell

Scanning the Clock Pins The AVR devices have many clock options selectable by fuses. These are: Internal RC

Oscillator, External RC, External Clock, (High Frequency) Crystal Oscillator, Low Fre-

quency Crystal Oscillator, and Ceramic Resonator.

Figure 120 shows how each oscillator with external connection is supported in the scan

chain. The Enable signal is supported with a general boundary-scan cell, while the oscil-

lator/clock output is attached to an observe-only cell. In addition to the main clock, the

timer oscillator is scanned in the same way. The output from the internal RC-Oscillator is

not scanned, as this oscillator does not have external connections.

Pxn

PUExn

ODxn

IDxn

TWIEN

OCxn

Slew-rate Limited

SRC

From

Cell

ClockDR

ShiftDR

Cell

From System Pin

To System Logic

FF1

1 2 ... 221 222 223 224 225 226 227 228 229 230 231 ... 297 298

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Rainbow-electronics ATmega64L Manual do Utilizador Página 226