The features available via the keypad are mentioned in the Spectrum 128 Introduction Manual that was included with every machine sold. The service manual for the Spectrum 128 is aimed at repair technicians and describes the circuitry and communications protocol used by the keypad. Extracts from both of these documents are reproduced below.

Spectrum 128 Introduction Manual

The Introduction Manual contains the following details relating to the keypad:

Setting Up - Page 3:

Spectrum 128 Introduction Manual - Setting Up

Getting Started - Page 4:

Spectrum 128 Introduction Manual - Getting Started

128 BASIC - Page 7:

Spectrum 128 Introduction Manual - 128 BASIC

Using The Calculator - Page 8:

Spectrum 128 Introduction Manual - Using The Calculator

Spectrum 128 Service Manual

The Service Manual specifies the offical names used for the various states in the keypad communications protocol.

Section 1 - System Description:

Spectrum 128 Service Manual - System Description

This section also contains the circuit diagram of the keypad (Figure 1.7):

Spectrum 128 Service Manual - Circuit Diagram

Section 5 - Parts List:

Spectrum 128 Service Manual - Parts List