Pinout info for the Revision A iMac's 'mezzanine' (aka PERCH) connector

The first version of the iMac had a strange connector on the underside ot the motherboard. A manufacturer for the connector (and subsequent mates to it) is Molex and the part number is 52760-1609. The original purpose of this port was to connect a logic analyzer and quickly diagnose board problems. It was intended to make servicing the boards easier. It was never intended at any time for an upgrade card, and thus, the PCI loads were calculated for that board with the intention of no real PCI load being present. As such there are pull down resistors on the board to 'tune' the performance of the bus for not having a load on the connector

This version of the iMac uses the MPC106 PCI controller that only outputs 32/33 or 32/66, meaning that only 32 bit PCI devices are supportred. The Blue and White G3’s had a PCI-PCI bridge that took 32/66 from the MPC106 and turned into 64/33 slots. In theory, if a PCI-PCI birdge was mated to the iMac, a full 64 bit PCI device could be supported. Adding an upgrade card would most likely require buffers to amplify the PCI signals without drawing too much current. This approach may weaken signal integrity and reduce performance.

Pins for the 'mezz' connector are identified (from my reverse engineering an iProRaid TV card) to be as follows:

1 - 41 - 81 - AD(01) 121 - Gnd
2 - 42 - 82 - AD(04) 122 - IRDY#
3 - 43 - 83 - AD(02) 123 - AD(20)
4 - 44 - 84 - AD(05) 124 -
5 - Gnd. 45 - Gnd 85 - 125 - AD(21)
6 - 46 - Gnd. 86 - +5V 126 - AD(17)
7 - 47 - 87 - AD(03) 127 - Gnd
8 - Gnd. 48 - 88 - AD(08) 128 - AD(18)
9 - Gnd. 49 - + 5V 89 - Gnd 129 - AD(22)
10 - 50 - 90 - AD(09) 130 -
11 - 51 - 91 - AD(06) 131 -
12 - Gnd 52 - 92 - 132 - AD(19)
13 - 53 - 93 - AD(07) 133 - AD(23)
14 - 54 - 94 - AD(10) 134 - C_BE/(03)
15 - 55 - 95 - +5V 135 - AD(27)
16 - 56 - 96 - AD(11) 136 - +5V
17 - 57 - 97 - AD(12) 137 - +5V
18 - 58 - 98 - Gnd138 - AD(24)
19 - 59 - 99 - AD(13)139 - AD(28)
20 - 60 - Gnd 100 - C_BE/(00) 140 - AD(25)
21 - 61 - Gnd 101 - Gnd 141 - AD(29)
22 - 62 -+5V 102 - 142 - Gnd
23 - Gnd 63 - INTA# 103 - AD(14) 143 -
24 - 64 - REQ# 104 - Gnd 144 - AD(26)
25 - 65 - 105 - AD(15) 145 - AD(30)
26 - Gnd 66 - GNT# 106 - 146 -
27 - 67 - Gnd 107 - 147 - Gnd
28 - 68 - Gnd 108 - C_BE/(01) 148 - AD(31)
29 - 69 - Rst# 109 - C_BE/(02) 149 -
30 - 70 - 110 - +5V 150 - +5V
31 - 71 - 111 - AD(16) 151 - Gnd
32 - 72 - IRQ/ 112 - PAR 152 -
33 - 73 - REQ# 113 - Gnd 153 -
34 - Gnd 74 - Gnd 114 - STOP# 154 - Gnd
35 - 75 - IDESL (?) 115 - FRAME# 155 - Gnd
36 - 76 - 116 - Gnd 156 -
37 - Gnd 77 - AD(00) 117 - +5V 157 - CLK
38 - 78 - 118 - DEVSEL 158 -
39 - 79 - Gnd 119 - TRDY# 159 - Gnd
40 - +5V 80 - Gnd 120 - Gnd 160 -

Anyone with good info to complete this table, please send a PM.

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DrBunsen's picture

"Diagnostic port" my a$$

The original purpose of this port was to connect a logic analyzer and quickly diagnose board problems. It was intended to make servicing the boards easier. It was never intended at any time for an upgrade card,

Heh. Didn't someone try and sneak this past SJ once before? Laughing out loud

DrBunsen's picture

BTW a mobo with Voodoo Mezz c

BTW a mobo with Voodoo Mezz card just sold on ebay.au

doug-doug the mighty's picture

that rots!

at least it was not the iProRAID or iProRAIDTV. I have been dying for one of these cards - it is key to an iMac hack I have planned for years.

Eudimorphodon's picture

Re: that rots!

doug-doug the mighty wrote:

at least it was not the iProRAID or iProRAIDTV. I have been dying for one of these cards - it is key to an iMac hack I have planned for years.

You could just make your life a *lot* easier and buy a Beige G3 All-In-One, you know. Three PCI slots gratis! ;^b

--Peace

doug-doug the mighty's picture

true...

...but my passion for the mezz slot is more hobby than crippling obstacle. I already have the hack planned and all I need is the iProRaid (or the iProRAIDTV) card - everything else I need is still available today in good supply. The alternative was to build my own card which I abandoned some time back thanks to some insight from dr. bob.

The AIO is a nice idea, but I only ever had one pass through my hands and I just did not like it as much as the early iMacs - that and everything else I have is B&W, even my desk chair! What I am shooting for here is the SCSI slots and the A/V capture on my Bondi.

Eudimorphodon's picture

Yeah, I know.

The suggestion was tongue in cheek, of course. Still, though... bleah. I guess I've just dealt enough with those tray-loader iMacs to be of the opinon that a sow's ear is a sow's ear, and installing SCSI and a BTTV848 capture chip isn't going to make it any more purse-like.

--Peace