The Maplin Electronic Circuits Handbook, 2nd Edition

MONOSTABLES AND BISTABLES 137

-+5V

L7405

i-7405

- 7405

2k2

Output

I

From other open-collector logic

Figure 6.18 Wired-NOR

configuration based on open-

collector logic gates

ENABLE A

ENABLE Β

3us line

Figure 6.19 Tri-state logic

configuration

the same output line (bus) should be driven into the high-impedance

state by taking their respective ENABLE inputs to logic 1. Figure

6.19 illustrates this principle.

Where not all of the inputs of a gate are connected or where not all

gates within a package are being used, one is sometimes left wondering

what to do with the unused connections. A TTL input left unconnected

almost invariably 'floats' to th ...