This is the pinout for Apple's (mostly) universal firmware module. As far as I can tell it was used from the NuBus Powermacs through the Beige G3 in their main professional machines. The consumer (LC/Performa) machines had other arrangements.
Disclaimer: I'm not responsible if you use this information to damage something or otherwise screw up. I might have made mistakes typing this. I might be insane. This pinout seemed to work for me. Keep in mind the effect hours with a multimeter, a couple of firmware modules and some ROM datasheets is likely to have had on my mental stability.
Power Surge (PS) is the generic name for the 7500, 8500, 9500 and clones and later family models. The 7200 uses the same ROM (yes, and the same code) and the same firmware module as the PS.
The Apple Network Server uses the same type of Firmware module as the Power Surge, though with different contents in the chips, of course.
The voltage supply pins of the Beige G3 are different from the earlier modules because the Beige G3 uses a 3.3V supply and the earlier machines use a 5V supply.
The pins of Apple's universal firmware module are numbered 1 through 160. There are 80 on each side. Usually modules will have some numbers silk screened on them to help you out. The module is a DIMM. Every pin is unique. Pins on opposite sides of the board are not connected the way they are on SIMMs.
From edge to notch to notch to edge, they go 1 - 30, 31 - 55, 56 - 80, flip sides, 81 - 110, 111 - 135 and 136 - 160.
The first column in the list below is the Beige pin. The second column is the Power Surge (PS) pin. I have not explicitly mapped out all the pins on the NuBus Mac ROM module, but I would expect the pinout to be very similar if not identical to the Power Surge pinout. I have confirmed that it follows the same basic pattern.
The firmware module is 64 bits wide. On early machines this is usually achieved with four 16 bit wide storage chips, although larger numbers of narrower chips were sometimes used. On the Beige G3 there are just two 32 bit wide ROM chips. No one makes anything like that anymore.
The HL, HH, LL and LH designations on the Power Surge data pins refer to which ROM chip those data pins connect to. So, for example, you'll find four ROM chips on the motherboard labeled with those four designators. The D0 HL pin in the ROM socket connects to the D0 pin on the HL ROM chip which is soldered to the motherboard. In the X500 series, chip 341S0171 = LL, 341S0170 = LH, 341S0169 = HL and 341S0168 = HH. In the Kansas: 341S0380 = HH, 341S0381 = HL, 341S0382 = LH, 341S0383 = LL.
On the original G3 ROM (revision A) 341S0402 = H and 341S0403 = L.
There is no ROM soldered to the motherboard, but the Beige G3 uses two 32 bit wide ROM chips. The L and H refer to the high and low ROM chips.
More notes at the bottom.
Pin Beige PS
1 NC Vcc
2 GND GND
3 Vpp? Vpp? (this would be used on a programmable module with old EEPROMs)
4 D16 L D0 HL
5 D17 L D1 HL
6 D18 L D2 HL
7 D19 L D3 HL
8 Vcc N/A
9 NC Vcc
10 Vcc NC
11 D20 L D4 HL
12 D21 L D5 HL
13 D22 L D6 HL
14 D23 L D7 HL
15 GND GND
16 D24 L D8 HL
17 D25 L D9 HL
18 D26 L D10 HL
19 D27 L D11 HL
20 Vcc NC
21 NC Vcc
22 NC? NC
23 D28 L D12 HL
24 D29 L D13 HL
25 D30 L D14 HL
26 D31 L D15 HL
27 GND GND
28 NC? NC
29 NC? NC
30 A2 A2
31 A4 A4
32 A6 A6
33 A8 A8
34 A10 A10
35 NC NC
36 NC NC
37 WE WE (For programmable modules, also may connect to pin 117)
38 OE H OE A1L (May also connect to pin 118)
39 NC NC
40 Vcc NC
41 NC Vcc
42 NC NC
43 GND GND
44 A12 A12
45 A14 A14
46 A16 A16
47 A18 A18
48 NC NC
49 NC NC
50 NC NC
51 NC NC
52 NC NC
53 GND GND
54 D16 H D0 HH
55 D17 H D1 HH
56 D18 H D2 HH
57 D19 H D3 HH
58 GND GND
59 NC Vcc
60 NC NC
61 D20 H D4 HH
62 D21 H D5 HH
63 D22 H D6 HH
64 D23 H D7 HH
65 GND GND
66 D24 H D8 HH
67 D25 H D9 HH
68 D26 H D10 HH
69 D27 H D11 HH
70 Vcc NC
71 NC Vcc
72 NC NC
73 D28 H D12 HH
74 D29 H D13 HH
75 D30 H D14 HH
76 D31 H D15 HH
77 GND GND
78 NC NC
79 Vcc NC
80 NC Vcc
81 NC Vcc
82 GND GND
83 NC NC (May be Vpp on programmable modules)
84 D0 L D0 LL
85 D1 L D1 LL
86 D2 L D2 LL
87 D3 L D3 LL
88 Vcc NC
89 NC Vcc
90 Vcc NC
91 D4 L D4 LL
92 D5 L D5 LL
93 D6 L D6 LL
94 D7 L D7 LL
95 GND GND
96 D8 L D8 LL
97 D9 L D9 LL
98 D10 L D10 LL
99 D11 L D11 LL
100 Vcc NC
101 NC Vcc
102 NC NC
103 D12 L D12 LL
104 D13 L D13 LL
105 D14 L D14 LL
106 D15 L D15 LL
107 GND GND
108 A0 A0
109 A1 A1
110 NC NC
111 A3 A3
112 A5 A5
113 A7 A7
114 A9 A9
115 _CE _CE
116 Vcc 1Kohm to GND?
117 NC OR WE for back of module on programmable modules, may also connect to 37
118 _OE L _OE all, also connects to 38
119 NC NC
120 Vcc NC
121 NC Vcc
122 NC NC
123 GND GND
124 A11 A11
125 A13 A13
126 A15 A15
127 A17 A17
128 NC NC
129 NC NC
130 NC NC
131 NC NC
132 NC NC
133 GND GND
134 D0 H D0 LH
135 D1 H D1 LH
136 D2 H D2 LH
137 D3 H D3 LH
138 Vcc NC
139 NC Vcc
140 NC NC
141 D4 H D4 LH
142 D5 H D5 LH
143 D6 H D6 LH
144 D7 H D7 LH
145 GND GND
146 D8 H D8 LH
147 D9 H D9 LH
148 D10 H D10 LH
149 D11 H D11 LH
150 Vcc NC
151 NC Vcc
152 NC NC
153 D12 H D12 LH
154 D13 H D13 LH
155 D14 H D14 LH
156 D15 H D15 LH
157 GND GND
158 NC NC
159 Vcc NC
160 NC Vcc
Notes:
1) CE (pin 115) can simply be tied low or not.
2) OE low (pin 118) and OE high (pin 38) do not need to be connected together on the firmware module--they're connected on the motherboard.
3) Pin 116 connects to the CE_ of the motherboard ROM on PS and 7200 machines. If you tie it high, it disables the motherboard ROM so that the module ROM/firmware can take over.
4) While pin 122 may be grounded on some Beige modules, connecting it to ground seems to disable support for more than 512 MB of RAM in the Beige.
5) The Beige will not work with 120 ns flash. 90 ns or faster is needed, although I haven't tested 100 ns.
6) The PowerSurge seems to work with 120 ns flash, but stick to 90 ns or better to be safe.
