What is it?

The Am9511A APU module is designed to work with the RC2014 Standard Bus and optionally with the RC2014 Extended Bus. Supporting logic is provided to ensure that the Am9511A APU is adapted to the RC2014 system clock, and to the Z80 control signals.

The Am9511A requires both +5V and +12V power supplies. To obtain +12V a switch-mode boost converter is provided. Consumption of between 50mA and 100mA from both +5V and +12 V supplies is typical, and the device packaging (24-pin ceramic DIL) is designed to dissipate up to 2W. It is normal for the Am9511A to operate HOT TO TOUCH and the APU Module is constructed with 4-layers and complete Vcc and GND layers to enable rapid heat sinking into the PCB.

Why did you make it?

The AMD Am9511 was the world's first Arithmetic Processing Unit, and the world's first commercially available 16-bit processor. It was cross licenced by Intel and sold as the Intel 8231 APU, which predated the 8087 FPU for the 8086 processors.

Even today, the Am9511A provides a worthwhile performance improvement for RC2014 based systems, in some cases leading to a 3.6x speed up of floating point applications.

What makes it special?

The Am9511A-1DC device operates at a maximum of 3MHz. Therefore to operate successfully with the RC2014 7.3728MHz system clock a 3:1 reduction of the clocking for the APU is required. A 50% duty 1/3 rate circuit has been constructed from two D flip-flops and a JK flip-flop, and several NOR gates.

The APU Module is primarily designed to be used with the z88dk development environment, where a floating point library for the Am9511A is available. Both z80 and 8085 CPUs are fully supported by this library.

Additionally, some support is available for up to 4x APU Modules for parallelised (vector or matrix) floating point processing.

Also, a modified version of Microsoft BASIC is also available which will offload mathematical functions for a slight speed increase, and also provide a built in hex upload routine for quick and easy z80 or 8085 hex file uploads. Note that this new BASIC only supports the 68B50 ACIA Serial Module, so will only work on the, RC2014 Mini, RC2014 Classic and RC2014 Classic ][.

The APU Module can optionally be equipped with an Intel 8231A APU, and it also works with the Intel 8085 CPU Module, and Microsoft BASIC.

The APU Module can either be operated with the RC2014 Standard Bus (single row header) or the Enhanced Bus (double row header). The Enhanced Bus option takes advantage of the /WAIT signal in the additional header pins. The Standard Bus option will require the user to either run a jumper cable between this module and the CPU, or to make a modification to CPU Module to connect the /WAIT signal out to the USER1 pin.

Update for 2023

The optional /WAIT capacitor C8 has been added to the PCB in space cleared by deleting the unused /NMI option.

Ordering Options

This is the Am9511A Module Printed Circuit Board (PCB) Only.

If you find the postage is too high, then please use the attached documentation to make your own, and share with others.