2nd slot on HP-46


Hello all,

I noticed a 2nd slot, right next to the display slot. What was the use of this? Was it possible to add buffered input as an option - hpmuseum.org says it wasn't?
machine is # 222



I had an HP46 for awhile before selling it (unfortunately).

I vaguely recall something 'interesting' on PCB....

Could you send/post a picture of the innards in that area?

The HP9805 'Algebraic Statistics Desktop' and the HP81 both share much in common with the HP46.

It perhaps could be some kinda ROM slot, slot for external plotter (on HP9805 calc), or a keyboard buffer option slot (used on HP81). Perhaps the PCB is common for all these variants...

From this HP Musuem's website's HP 9805 commentary:

Key and ROM Blocks

....The HP 9805 took this idea a step further with a plug-in block of keys that also contained the appropriate ROM. The 15 keys on the left side of the machine could easily be replaced.

In addition one ROM block without keys could be added under the printer cover. Functions in this block were accessed by the CALL key and other program-oriented keys on the keyboard

The HP9805 could also interface to a plotter somehow; this picture (http://www.hpmuseum.org/9805.jpg) shows a 9805 calc with what's described as "Another picture of HP-9805. (An additional key block and an interface card are sitting next to the calculator.)"

On the HP81 'business' calc, a buffered keyboard was sold as an option. As the text on Museum's HP81 page
(http://www.hpmuseum.org/hp81.htm) says,

Unlike the HP46, the HP81 had the option of a buffered keyboard. (Probably only offered on the 81, because it could take some time to solve pre-programmed business problems.) ......

$925 with printer only
$1025 with printer and LED display
$1150 with printer & buffered keyboard but no LED display
$1250 with printer, buffered keyboard, LED Display

I don't know if most HP81s were or weren't sold w/keyboard buffering.

Perhaps this helps...

Bill Wiese

San Jose

['123' to delete]

Edited: 29 Mar 2005, 2:46 p.m.


Here are some pictures of the inside of an 81 with printer, LED display and keyboard buffer and a 46 with printer and LED display. They seem to share a common motherboard that is populated with different chips but has just a single expansion slot. The 81 uses this slot for a combination keyboard buffer and LED display card -- note how the keyboard cable daisy chains through this card on the 81. Also note how there's an extra soldered-in wire on the back of this card going to the motherboard. Clearly this made the buffer not a user installable upgrade.




Having reverse-engineered the HP46 and HP81 for the HPCC schematics CD-ROM, I can confirm that they do share the mainboard, with different ROMs fitted (and IIRC extra RAM on the 81).

I don't recall there being a second edge connector on the board -- if there was then it'll be in the schematics which I can check later.

Neither of the machines I borrowed for this had the buffered keyboard option, so I can't tell you anything about that.

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