NEO-253

NEO-253 chip found on a SLOT4F board.

Quintuple 74HC253 4-to-1 multiplexers with common select lines, making 10 switches in one chip. Only (?) used on second revision 4-slot MVS systems.

• SLOT4F @ 5E: SDD, PWAIT0, and PWAIT1 mux.
• SLOT4F @ 5D: ?
• ...

Pinout

OpenOffice Draw file: File:Neo-253.odg

Draft:

54,55: selects

Muxes (0,1,2,3,out):

• 60,61,62,63,59?
• 49,50,51,52,44?
• 45,46,47,48,43?
• 37,38,39,40,41?
• 33,34,35,36,28?
• 29,30,31,32,27?
• 20,21,22,23,24?
• 12,13,14,15,11?
• 4,5,6,7,?
• 64,1,2,3,?

63:sdd7 slot 4, 52 48 40 36 32 23 15:sdd0 slot 4

62:sdd7 slot 3, 51 47 39 35 31 22 14:sdd0 slot 3

61:sdd7 slot 2, 50 46 38 34 30 21 13

60:sdd7 slot 1, 49 45 37 33 29 20 12

9/10: ?

out CN9:59 44 43 41 28 27 24 11

7 6 5 4: PWAIT1 4-3-2-1. 3 2 1 64: PWAIT0 4-3-2-1.

8? 16? 17? 18? 19? 42? 53?