Product Overview
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. Chip body and all 28 pins are clean, straight, and untarnished - confirmed by inspection. Markings read Z1L06 / 1820-2301 / SL0074-00 / 8126 Y on one face and HPHILAC127ME on the other. Date code 8126 Y indicates manufacture in week 26 of 1981. No corrosion, bends, or chips visible.
Ships same business day from our Idaho warehouse. Carefully packed for safe arrival.
No hassle resolution if there is an issue. Serving customers since 1999.
Product Overview
Zilog Z80 CTC (Counter/Timer Circuit) sold under HP part number 1820-2301. This IC is a programmable peripheral designed to work directly with the Z80 CPU, providing four independent channels that can be configured as event counters or interval timers. Each channel can generate interrupts or output signals on zero count, offloading timing and counting tasks from the main processor. Package is a standard 28-pin DIP. Operates on a single +5V supply and interfaces with the Z80 data bus and control signals including IORQ, M1, RD, and chip select lines. Clock speed grade is not confirmed - verify against your system's requirements before ordering. The HP part number 1820-2301 was used in HP instruments and systems of the late 1970s and early 1980s that incorporated Z80-based designs.
Key Features
- Zilog Z80 CTC - HP part number 1820-2301
- Four independent counter/timer channels
- 28-pin DIP package - standard through-hole footprint
- Single +5V supply
- Interfaces directly with Z80 data bus and control signals (IORQ, M1, RD, CS)
- Each channel programmable as event counter or interval timer
- Interrupt-driven operation - frees Z80 CPU from polling
- 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
- Replacement or repair of HP instruments and systems using the 1820-2301 part number
- Z80-based retro computer repair - TRS-80, ZX Spectrum, Osborne 1, and related systems
- Arcade cabinet restoration - Pac-Man and other Z80-based boards that relied on CTC timing
- RC2014 modular Z80 computer builds and other modern Z80 homelab projects
- Baud rate generation for Z80 SIO serial communication
- Event counting and interval timing in Z80 embedded system projects
Frequently Asked Questions
Is this a direct replacement for other Z80 CTC parts like the Z8430 or Z0843006?
Functionally, yes - the 1820-2301 is HP's part number for a Zilog Z80 CTC, the same device family as the Z8430 and Z84C30. However, clock speed grade and NMOS vs. CMOS variant are not confirmed on this unit. Match the 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 does not have a ZC/TO output pin - only an interrupt request is available on that channel. This is a hardware limitation of the Z80 CTC design, not specific to this unit.
What is the maximum clock speed this part supports?
Not confirmed. The Z80 CTC family includes variants rated at 2.5 MHz, 4 MHz, 6 MHz, 8 MHz, and 10 MHz. Speed grade is not legible from the markings visible on this unit. Verify against the datasheet for the specific variant before use in a speed-sensitive application.
Is a datasheet or documentation included?
Not included. The chip only.
Can this be used in non-Z80 systems?
The Z80 CTC is designed for the Z80 bus architecture. Use in non-Z80 systems requires additional interface logic and is not a straightforward substitution.
Sitting unused since 1981 is a long time to wait for the right repair bench - but here it is, pins still bright, ready to put four channels back to work in whatever Z80 project actually needs them.
