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,..,,.,....,"'"' in the block from 65520 to 65535 will be decoded by the<br />
decoder ( SN7 4154) . Since the decoder only provides you<br />
the "bottom" eight addresses, only addresses from 65520 to<br />
527 will be available.<br />
your computer on. If you are running a program, press the<br />
RESET key. Use the logic probe to test the eight address outputs at<br />
e ADDRESS socket. Are any of the decoder outputs active ( pulsg)<br />
Since you are not running a program, is this what you would<br />
xpect<br />
Two of the outputs should be active, 0 and 4, corresponding to<br />
65520 and 65524. While the computer is not running a<br />
program, it is executing many assembly-language steps that<br />
nitor the keyboard, etc. Remember that the address decoding ciris<br />
always decoding addresses.<br />
Wire the circuit shown in Fig. 6-4. Be sure that you connect the<br />
wer pin, pin 14, to +5 volts and the ground pin, pin 7, to power<br />
Ro<br />
7'<br />
10<br />
SN7 402(ALL)<br />
13<br />
*DECODER SOCKET POSITIONS<br />
und. Refer to Fig. 6-3 for the pin configuration of the SN7 402.<br />
may substitute an SN74LS02 for this chip. The outputs of the<br />
es, A, B, and C, are not connected to any circuit at this time.<br />
hange the switch settings on the dip switches for bits Al5-A4 for<br />
address of 49312. This is 11000000 101000002, and you should ige<br />
the four least-significant bits. What range of addresses will be<br />
Hable when the address switches are set this way
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