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

Submitted by doug-doug the mighty on August 31, 2004 - 12:32pm

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:
[table][tr][td]1 - [/td][td]41 - [/td][td]81 - AD(01) [/td][td]121 - Gnd[/td][/tr]
[tr][td]2 - [/td][td]42 - [/td][td]82 - AD(04) [/td][td]122 - IRDY#[/td][/tr]
[tr][td]3 - [/td][td]43 - [/td][td]83 - AD(02) [/td][td]123 - AD(20)[/td][/tr]
[tr][td]4 - [/td][td]44 - [/td][td]84 - AD(05) [/td][td]124 -[/td][/tr]
[tr][td]5 - Gnd. [/td][td]45 - Gnd [/td][td]85 - [/td][td]125 - AD(21)[/td][/tr]
[tr][td]6 - [/td][td]46 - Gnd. [/td][td]86 - +5V [/td][td]126 - AD(17)[/td][/tr]
[tr][td]7 - [/td][td]47 - [/td][td]87 - AD(03) [/td][td]127 - Gnd[/td][/tr]
[tr][td]8 - Gnd. [/td][td]48 - [/td][td]88 - AD(08) [/td][td]128 - AD(18)[/td][/tr]
[tr][td]9 - Gnd. [/td][td]49 - + 5V [/td][td]89 - Gnd [/td][td]129 - AD(22)[/td][/tr]
[tr][td]10 - [/td][td]50 - [/td][td]90 - AD(09) [/td][td]130 -[/td][/tr]
[tr][td]11 - [/td][td]51 - [/td][td]91 - AD(06) [/td][td]131 -[/td][/tr]
[tr][td]12 - Gnd [/td][td]52 - [/td][td]92 - [/td][td]132 - AD(19)[/td][/tr]
[tr][td]13 - [/td][td]53 - [/td][td]93 - AD(07) [/td][td]133 - AD(23)[/td][/tr]
[tr][td]14 - [/td][td]54 - [/td][td]94 - AD(10) [/td][td]134 - C_BE/(03)[/td][/tr]
[tr][td]15 - [/td][td]55 - [/td][td]95 - +5V [/td][td]135 - AD(27)[/td][/tr]
[tr][td]16 - [/td][td]56 - [/td][td]96 - AD(11) [/td][td]136 - +5V[/td][/tr]
[tr][td]17 - [/td][td]57 - [/td][td]97 - AD(12) [/td][td]137 - +5V[/td][/tr]
[tr][td]18 - [/td][td]58 - [/td][td]98 - Gnd[/td][td]138 - AD(24)[/td][/tr]
[tr][td]19 - [/td][td]59 - [/td][td]99 - AD(13)[/td][td]139 - AD(28)[/td][/tr]
[tr][td]20 - [/td][td]60 - Gnd [/td][td]100 - C_BE/(00) [/td][td]140 - AD(25)[/td][/tr]
[tr][td]21 - [/td][td]61 - Gnd [/td][td]101 - Gnd [/td][td]141 - AD(29)[/td][/tr]
[tr][td]22 - [/td][td]62 -+5V [/td][td]102 - [/td][td]142 - Gnd[/td][/tr]
[tr][td]23 - Gnd [/td][td]63 - INTA# [/td][td]103 - AD(14) [/td][td]143 -[/td][/tr]
[tr][td]24 - [/td][td]64 - REQ# [/td][td]104 - Gnd [/td][td]144 - AD(26)[/td][/tr]
[tr][td]25 - [/td][td] 65 - [/td][td]105 - AD(15) [/td][td]145 - AD(30)[/td][/tr]
[tr][td]26 - Gnd [/td][td]66 - GNT# [/td][td]106 - [/td][td]146 -[/td][/tr]
[tr][td]27 - [/td][td]67 - Gnd [/td][td]107 - [/td][td]147 - Gnd[/td][/tr]
[tr][td]28 - [/td][td]68 - Gnd [/td][td]108 - C_BE/(01) [/td][td]148 - AD(31)[/td][/tr]
[tr][td]29 - [/td][td]69 - Rst# [/td][td]109 - C_BE/(02) [/td][td]149 -[/td][/tr]
[tr][td]30 - [/td][td]70 - [/td][td]110 - +5V [/td][td]150 - +5V[/td][/tr]
[tr][td]31 - [/td][td]71 - [/td][td]111 - AD(16) [/td][td]151 - Gnd[/td][/tr]
[tr][td]32 - [/td][td]72 - IRQ/ [/td][td]112 - PAR [/td][td]152 -[/td][/tr]
[tr][td]33 - [/td][td]73 - REQ# [/td][td]113 - Gnd [/td][td]153 -[/td][/tr]
[tr][td]34 - Gnd [/td][td]74 - Gnd [/td][td]114 - STOP# [/td][td]154 - Gnd[/td][/tr]
[tr][td]35 - [/td][td]75 - IDESL (?) [/td][td]115 - FRAME# [/td][td]155 - Gnd[/td][/tr]
[tr][td]36 - [/td][td]76 - [/td][td]116 - Gnd [/td][td]156 -[/td][/tr]
[tr][td]37 - Gnd [/td][td]77 - AD(00) [/td][td]117 - +5V [/td][td]157 - CLK[/td][/tr]
[tr][td]38 - [/td][td]78 - [/td][td]118 - DEVSEL [/td][td]158 - [/td][/tr]
[tr][td]39 - [/td][td]79 - Gnd [/td][td]119 - TRDY# [/td][td]159 - Gnd[/td][/tr]
[tr][td]40 - +5V [/td][td]80 - Gnd [/td][td]120 - Gnd [/td][td]160 - [/td][/tr]
[/table]

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

Comments

DrBunsen's picture

Submitted by DrBunsen on December 21, 2006 - 9:04am.

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? Biggrin

DrBunsen's picture

Submitted by DrBunsen on January 3, 2007 - 6:55am.

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

doug-doug the mighty's picture

Submitted by doug-doug the mighty on January 3, 2007 - 7:47am.

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

Submitted by Eudimorphodon on January 3, 2007 - 10:54am.

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

Submitted by doug-doug the mighty on January 3, 2007 - 11:23am.

...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

Submitted by Eudimorphodon on January 3, 2007 - 11:36am.

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