Zilog Z80 CTC 4-Channel Counter Timer IC HP 1820-2301 28-Pin DIP NOS

Zilog Z80 CTC Counter/Timer Circuit - HP Part 1820-2301 - 28-Pin DIP - Four Independent Channels - Unused NOS

Condition

Unused NOS, sourced from an electronics distributor consolidating inventory. Photographed on pink antistatic film from four angles. The top face carries the Zilog logo followed by ZILOG, then 1820-2301, SL0074-00 and 8126 Y, a date code placing manufacture in week 26 of 1981. The opposite face is stamped HPHILAC127ME. All 28 pins are present, straight, full length and bright with factory tinning - no solder buildup on the tips, no socket scuffing, no bends or splay. The black plastic body is clean, with crisp molded dimples and no chips, cracks, or corrosion.

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Product Overview

Zilog Z80 CTC (Counter/Timer Circuit) carrying Hewlett-Packard part number 1820-2301, the number HP used for this device inside its own late-1970s and early-1980s Z80-based instruments and systems. The CTC is a programmable peripheral built to sit directly on the Z80 bus, giving four independent channels that can each be configured as an event counter or an interval timer, generating an interrupt or an output on zero count and taking timing work off the main processor. The package is a standard 28-pin DIP on a single +5V supply, interfacing with the Z80 data bus and control lines including IORQ, M1, RD, and chip select. This particular unit is double-marked: the Zilog logo and 1820-2301 / SL0074-00 / 8126 Y on the top face, HPHILAC127ME on the reverse, so the same chip answers to both the manufacturer's family and HP's instrument bill of materials. Clock speed grade and process variant are not printed in a form that identifies them here - verify both against the datasheet before use.

Key Features

• Zilog Z80 CTC counter/timer - HP part number 1820-2301
• Four independent counter/timer channels
• 28-pin DIP package - standard through-hole footprint
• Single +5V supply
• Interfaces directly with the Z80 data bus and control signals (IORQ, M1, RD, CS)
• Each channel programmable as an event counter or an interval timer
• Interrupt-driven operation - frees the Z80 CPU from polling
• Top-face markings: Zilog logo, ZILOG, 1820-2301, SL0074-00, 8126 Y
• Reverse-face marking: HPHILAC127ME
• Date code 8126 Y - manufactured week 26 of 1981
• Clock speed grade: Not confirmed - verify against datasheet before use
• NMOS or CMOS variant: Not confirmed - verify against datasheet before use

Applications

• Instrument technician repairing a vintage HP unit whose board calls out 1820-2301 by that exact number
• Retro computer restorer bringing a Z80 machine such as a TRS-80, Osborne 1, or ZX Spectrum peripheral back to service
• Arcade board repair tech chasing timing and interrupt faults on a Z80 cabinet PCB
• RC2014 homelab builder adding a CTC card for baud rate generation alongside a Z80 SIO

Frequently Asked Questions

Is this a direct replacement for a Z8430 or Z84C30 Z80 CTC?

Functionally it is the same device - 1820-2301 is HP's part number for a Zilog Z80 CTC, the same family as the Z8430 and Z84C30. Clock speed grade and NMOS versus CMOS process are not confirmed on this unit, so match speed grade and process type to your system before substituting.

Does Channel 3 have a ZC/TO (Zero Count/Timeout) output?

No. Channel 3 on the Z80 CTC brings out only an interrupt request, not a ZC/TO pin. That is how the Z80 CTC was designed, not a limitation of this particular chip.

What speed grade is it?

Not confirmed. The Z80 CTC family spans 2.5 MHz, 4 MHz, 6 MHz, 8 MHz, and 10 MHz variants, and nothing in the markings visible on this unit identifies the grade. Verify against the datasheet for your variant before using it in a speed-sensitive design.

What actually ships, and is there any documentation?

The chip only. No tube, no datasheet, no application notes. The four photographs are the record of what you are buying, including both marked faces.

Why buy one or two of these instead of a forced lot from a bulk seller?

A CTC is a part you count out, not a part you stockpile. One chip puts a dead channel back on a Z80 board, two gives you a spare in the drawer, and we hold enough of these to sell you that exact number instead of a tube of twenty-five you will never finish. Shipping is $8 flat rate, free once the order passes $28, and orders leave our Idaho warehouse the same or next business day.

One chip, two faces: Zilog's logo and name up top with HP's 1820-2301 stamped right under it, HPHILAC127ME on the reverse. Four channels that never counted a single event yet - the next Z80 bus you drop it into gets all of them.