CHA256: Difference between revisions

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(Created page with "===C ROMs=== Up to 8 * 32Mbit ROMs (27C322) can be used for a maximum of 256Mbit. 27C800/27C160 can also be used depending on jumper configuration. The size of largest ROM i...")
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Revision as of 19:09, 18 August 2012

C ROMs

Up to 8 * 32Mbit ROMs (27C322) can be used for a maximum of 256Mbit. 27C800/27C160 can also be used depending on jumper configuration.

The size of largest ROM is selected using a pair of jumpers. The rest should be left unconnected.

Largest C ROM Jumper set
8Mbit J5+J6
16Mbit J7+J8
32Mbit J9+J10

A NEO-273 and a LS74 are used to address C ROM. The LS74 provides the 2 most significant bits. The LS139 enables one of four pairs of C ROMs using 2 address inputs depending on which 2 jumpers are connected.

J5 J7 J9 ?
ROM number LSB is A19 ROM number LSB is A20 ROM number LSB is LS74 Q2 (A21 ?) ?
J6 J8 J10 ?
ROM number MSB is A20 ROM number MSB is LS74 Q2 (A21 ?) ROM number MSB is LS74 Q1 (A22 ?) ?