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HP LogicDart CPU?
09-23-2020, 12:39 PM (This post was last modified: 09-23-2020 01:24 PM by J-F Garnier.)
Post: #11
RE: HP LogicDart CPU?
(09-22-2020 06:09 PM)Jonathan Busby Wrote:  Thanks for all the informative replies! Smile I'll edit the Wikipedia article accordingly and remove the reference to handheld logic analyzers.

I was re-reading the article and was intrigued by the reference to the Saturn processor in the ThinkJet (and in the IPC built-in printer).
So I had a look at the ThinkJet service manual since this was new to me.

The Saturn is never mentioned in the service manual but surprising the Saturn bus appears in the schematics to drive RAM/ROM chips from the 1LJ7 control IC:

The RAM is a 1LK4 (1LG8 in the IPC) similar to the HP-71 1kbyte RAM chips,
the ROM is 1LG7 16kbyte ROM similar to the HP-71 ROM chips.
Curiously, the RAM/ROM chips are housed in big DIP28 packages.

So this could suggest that a Saturn core is used in the 1LJ7 control IC.

But referring to the HP Journal articles on the ThinkJet (May 1985), under the title "Custom VLSI Microprocessor System" , we can read (emphasis added):

"The ThinkJet Printer electronics are based on a custom HP integrated circuit that is a single-chip microprocessor system with a CPU, RAM, ROM, interface, timers, and I/O in one 48-pin package.[..]
Communication with external RAM and ROM is accomplished through a custom 6-bit interface originally designed for the HP-71 Handheld Computer."


"This architecture uses predesigned macrocells combined with specialized circuitry for special applications. The macrocells
include a high-speed control-oriented 8-bit CPU, a configurable mask-programmed ROM, a configurable RAM,
a programmable timer, an HP-IL interface, a crystal oscillator, a 4-bit test bus, and general-purpose I/O (GP-IO) pad cells.
The ThinkJet IC uses two timers, 160 bytes of RAM, 10K bytes of ROM."

Elsewhere, we can read:

"The character ROM and the buffer RAM are both HP custom parts chosen because of their availability from the
development of an earlier HP product
and their minimum number of interface lines. The character ROM is structured
in 4-bit nibbles , an efficient match for the 12-dot-high printhead column and its column-by-column character font representation.
The buffer RAM is also structured in nibbles, which is useful during the accumulation and printing of bit-mapped graphics data."

So the ThinkJet control IC reused the HP-71 Saturn bus for the external RAM (character buffer) and ROM (character bitmap).
But there is no Saturn processor inside the 1LJ7. At least no evidence for it, and strong presumptions for a classic 8-bit microcontroller.

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Messages In This Thread
HP LogicDart CPU? - Jonathan Busby - 09-19-2020, 08:43 PM
RE: HP LogicDart CPU? - David Bengtson - 09-20-2020, 01:20 AM
RE: HP LogicDart CPU? - teenix - 09-20-2020, 10:00 PM
RE: HP LogicDart CPU? - J-F Garnier - 09-21-2020, 08:48 AM
RE: HP LogicDart CPU? - Jake Schwartz - 09-21-2020, 01:22 PM
RE: HP LogicDart CPU? - rprosperi - 09-21-2020, 05:19 PM
RE: HP LogicDart CPU? - Jonathan Busby - 09-22-2020, 06:09 PM
RE: HP LogicDart CPU? - J-F Garnier - 09-23-2020 12:39 PM
RE: HP LogicDart CPU? - Jonathan Busby - 09-22-2020, 06:20 PM
RE: HP LogicDart CPU? - Didier Lachieze - 09-22-2020, 06:56 PM
RE: HP LogicDart CPU? - Jonathan Busby - 09-22-2020, 07:00 PM

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