Big box of PCB’s #5

Another big box of PCB’s arrived from jlcpcb this week.

In this box are my first add-on designs for the Raspberry Pi RP2040 based PICO module and also the Raspberry Pi 400 computer. So hopefully I will write about these in the next few posts.

As well as the Raspberry Pi stuff there where also some RC2014 boards as well.

As always, I’ll put them up to my Tindie shop

RC2014 a simple ROM/RAM card

It’s been a while since we published any thing new for the RC2014 architecture.

This is a simple combined ROM and RAM card designed to work with the RC2014 bus. This is an experimenters board. There is no fancy memory paging etc., it’s simple memory architecture was designed to be flexible and allow the user to experiment with other CPU architectures on the RC2014 bus. It was originally designed to work with our 8052 CPU.

It features

• enhanced RC2014 bus
• Selectable memory* options 8K, 16K or 32K
• Board can be used as RAM only or ROM only or both.
• Options for nMRD/nMWR or nRD/nWR signals
• Option for 27C512 with Hi/Lo ROM (A15) select
• IC Decoder 74xx138 using A15/A14/A13 (with extra options for A13 & A14)
  8 or 16-bit wide data bus**
• moveable memory positions (i.e. ROM can be at top or bottom memory space)

A couple of important notes:
* Both ROM and RAM memories must be the same size.
** see explanation below

The option for either nMRD and nMWR (nRD and nWR or’ed with nMREQ) signals or nRD and nWR only signals when IC3 (74xx32) is fitted or not fitted allows for experimenting with other CPU Read/Write architectures.

Notably, the enhanced RC2014 bus features a 16-bit data bus. The card can use this enhancement by allowing the selection of the high or low 8-bit portion of 16-bit data bus. This allows the user to experiment with 16-bit CPU’s such as 68000 or 8086 when two cards are used together.

It’s schematic is here

 

Big box of PCB’s

This week saw the arrival of another big box of PCB’s. A lot of PCB’s. Some old but many new.

Arriving where some new stock of RC2014 prototype board, prototype plus boards and extender boards which I sell on Tindie.

Also in the box where some new board designs. No new RC2014 PCB’s this time but some boards for the ZX Spectrum and Commodore 64 computers. I’ll share more details of these in the coming days and weeks.

Time to break out the soldering iron 🙂

Here’s my Tindies store.

RC2014 enhanced prototype board now on Tindie

I’m please to announce that the enhanced prototype board/PCB for the RC2014 Bus I blogged about back in May is now on Tindie.

Also it’s schematic is here.

RC2014 enhanced prototype board

If you’re into making I/O cards for the RC2014 than this enhanced prototype board might be of interest to you.

It features circuitry (see schematic) to for selectable decoding the I/O address and also gates to generate !IORD and !IOWR signals, as well as two spare OR gates.

The IC’s used are:

74LS32 Quad OR gate
74LS688 Octal (8-bit) magnitude comparator

Big Box of PCB’s

Earlier in the month I got big box of PCB’s for the most recent RC2014 boards I’ve been working on.

In amongst the PCB’s were a couple or three new designs. The first is an enhanced prototyping board. As well as lots of PCB pads for building stuff it also features some decoding logic to make your design a little easier. The other PCB was for a Z80 PIO digital input/output card and the final new PCB was for a minimal chip computer inspired by Grant Searle popular Z80 design but featuring an enhanced RC2014 bus (x3).

Z80 SIO2 Dual-UART Card for RC2014 bus (with clock)

Following on from last months Z80 CPU module for the RC2014 bus, here is a dual-serial SIO UART board.

So what makes it special?

It will work with either the standard RC2014 bus or the latest enhanced bus where all the Z80 CPU signals are available.

It includes several options for generating a Baud-Rate clock clock: Crystal, Oscillator or taken from RC2014 back plane.

The schematic is here:

and you can find it on Tindie here:

Z80 CPU Card for RC2014 (with clock and reset)

This is the Z80 CPU module I demonstrated a few months ago. It is designed to work with the RC2014 bus.

So what makes it special? Well, the module includes a number of extra features and enhancements designed to simplify a system build. These include:

It will work with either the standard RC2014 bus or the latest enhanced bus where all the Z80 CPU signals are available.

It includes several options for generating a signal clock: Crystal, Oscillator or taken from RC2014 back plane.

A reset circuit is included.

And the signals INT, NMI, BUSRQ and WAIT feature 10K pull-up resistors.

The schematic is here:

and you can find it on Tindie here:

8052 CPU card for RC2014 Bus part 2

It’s been a while since I posted about the 8052 CPU card for RC2014 Bus and heres a update to where i got to with this interesting RC2014 project.

The original 8052’s are still available but originally used UV erasable EPROM or OTP PROM for their program memory. So instead I’ve been using a modern FLASH memory version of the 8052, a AT89C5252 with great success.

The original 8052-BASIC has was good but had a number of software bugs. Fortunately, there had been a number of improvements over the years and the version I’ve been using is V1.31 which can be found here:

8052-BASIC needs a couple of K’s of RAM to operate. For this I’ve been using a standalone 32K-byte SRAM card.

Common TTL and CMOS Logic Gates

I been using a lot of TTL and CMOS logic gates in my recent RC2014 circuits and after realising that I had loaned out my much used copies of TI’s TTL Logic data books some time again and never got them back so to help me I created this quick comparison table for the common TTL and CMOS logic gates.

For completeness here’s a logic truth table: