5-7
5.3 Parallel Interface (IEEE 1284-C Connector)
The parallel interface is a bidirectional Centronics interface (nibble mode of the IEEE 1284 standard is supported).

5.3.1 Hardware requirements

Signal levels: TTL-compatible
0.0 to +0.4 V for low-level
+2.4 to +5.0 V for high-level
Input circuit: SN74LS14 or equivalent
Figure 5.5 shows the parallel interface input circuit.
+5 V
1 k
22
100 pF
+5 V
1.2 k
Data Strobe
Input Prime
(Auto Feed XT)
(Select In)
Data 1-8
22

Figure 5.5 Parallel interface input circuit

Figure 5.6 Parallel interface output circuit

Output circuit: SN74LS244 or equivalent
Figure 5.6 shows the parallel interface output circuit.
+5 V
1.2 k
22