Embedded System Interfacing

Appendix A

TTL Logic

Abstract

This chapter reviews TTL logic characteristics built with bipolar transistors. As with CMOS, logic levels, current drive capability, and timing are critical requirements for interfacing logic.

Keywords

Digital logic; TTL; Bipolar transistor; Logic levels

A.1 Introduction

TTL logic [58] is based on bipolar transistors. TTL is less common today but the comparison to CMOS helps to underline why we need to adhere to certain specifications. Many different logic families have been created with different advantages and design characteristics.

A.2 TTL Logic Circuits

Fig. A.1 shows two types of bipolar transistors: NPN and PNP. The three terminals are known as the base, emitter, and collector. The base terminal of ...