Microprocessors

1
Microprocessors

• Common TTL Devices used in Microprocessor Systems

2
Decoders

• Dual 2-to-4 Decoder (74XX139)

3-to-8 Decoder (74XX138)
3
Buffers

• Octal Buffer (74XX244)

Octal Bidirectional Buffer (74XX245)

• If G 1 then A(7..0) Hi-Z and B(7..0) Hi-Z
  
• else (if G 0) and DIR 0
• then A(7..0) B(7..0)
• else (if G 0) and DIR 1
• then B(7..0) A(7..0)

• If E1 0 then Y(3..0) I(3..0)
• else Y(3..0) Hi-Z (i.e Open)
• If E2 0 then Y(7..4) I(7..4)
• else Y(7..4) Hi-Z (i.e Open)

4
Latches

• Octal Latch (74XX373, 74XX573)

• If E 1 then the data at the D inputs D(7..0)
  is latched into the flip-flops.
• If E 0 then the outputs of the flip-flops do
  not change, irrespective of the data at the D
  inputs D(7..0).
• If OE 0 then the outputs of the flip-flops
  appear at the Q(7..0) outputs,
• else Q(7..0) Hi-Z (i.e Open)

5
Octal Buffers