Transcript CSE22MAL - Test Page for Apache Installation

ELE22MIC Lecture 9
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MULTIPLEXOR - DATA SELECTOR
DEMULTIPLEXOR - DATA DISTRIBUTOR
Parallel to Serial Data Conversion
External Address Bus Latching
Address Strobe timing Diagram
Address Decoding using a 74ls138
Serial Peripheral Interface - SPI
Multiplexor - Data Selector
• Multiplex (MUX) many inputs to one output
• Switch selects the one signal source from
many input signals.
• Like Stereo HiFi source selection switch
Two Input Multiplexor
Two Input Mux
Truth Table
Select Output
0 Input 0
1 Input 1
Output = (Input0 & Select#)
| (Input1 & Select)
Four Input Multiplexor
4 Input Multiplexor
Truth Table
Select Line:
1
0 Output
0
0 Input 0
0
1 Input 1
1
0 Input 2
1
1 Input 3
Eight Input Multiplexor
Eight Input Multiplexor
Truth Table
Select Line: Output
2
1
0
0
0
0 Input 0
0
0
1 Input 1
0
1
0 Input 2
0
1
1 Input 3
1
0
0 Input 4
1
0
1 Input 5
1
1
0 Input 6
1
1
1 Input 7
74F151 8-Input MUX
74F151 8-Input MUX
Pin Names and Loading / Fanout
Mux vs DeMux
Parallel I/O
External Address Latch
• The Address Bus (Bits 0..7) and Data Bus (Bits
0..7) are multiplexed onto Port C when in expanded
mode - external RAM, ROM & Peripherals
• We want to extend the Address Bus external to
the 68HC11 - MAR is presented on C0..PC7/A0..A7/D0..D7 pins
• The 68HC11’s AS pin strobes high to load the
address into the external address latch.
• The address latch presents the address onto the
system’s external address bus.
External Address Latch
Address Strobe Timing Diagram
Applications of a de-multiplexor
• The Memory Chip Select device used on the
original IBM PC is a 74LS138 de-multiplexor.
• The 74LS138 is used to activate 1 of 8 lines
based on the conditions of the three binary
select inputs A, B & C, and the three enable
inputs.
• The 74LS138 Outputs are “Active Low”.
74LS138 8-Output DEMUX
De-Multiplex one input to many
outputs -Reverse operation of a
multiplexor
74LS138 Truth Table
DeMultiplexor
• The 74LS138 can be
implemented by the
logic shown.
• The 54LS138 is identical in
function, but can operate over
the “Mil-spec” -55°C to
125°C Temperature Range.
• The 74LS138 can operate
over the Commercial 0°C 70°C Temperature Range.
Memory
Select
Address Decoding & Chip Select
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A15 -> G1#, E -> G, A14 -> A2, A13 -> A1
R/W# -> A0
Chip is enabled when A15 = 0 & E is High
Y2 = (A14#) & (A13) & Write (R/W#=0) & E
Y3 = (A14#) & (A13) & Read (R/W#=1) & E
Y4 = (A14) & (A13#) & Write (R/W#=0) & E
Y5 = (A14) & (A13#) & Read (R/W#=1) & E
Write Data Timing Diagram
68HC11 Flash Technology (1)
68HC11 Flash Technology (2)
Erasure of Cells is performed by providing a tunnelling
voltage to the control gate which causes the charge on the
floating gate to be removed. When read, each cell returns a
logical ‘1’ value.
68HC11 Flash Technology (3)
Programming of Cells is performed by providing a
tunnelling voltage to the control gate which causes the
charge to be placed on the floating gate. The write
process writes the ‘0’s into each cell.
68HC11 I/O & Control Bits (2)
Parallel to Serial Conversion (1)
• Many digital systems use parallel binary data
communication for speed (eg CPU data bus,
printer etc), but when large distances are to be
covered, the number of lines required makes
the parallel transmission costly and thus
undesirable.
• Referring to the schematic on the next page: A multiplexor
can be used convert parallel data to serial data. Parallel data
can be latched into the 74F373 gate, then output as a serial
data stream from the 74F151 as a binary count sequence is
created by the 74LS160.
Parallel to Serial Conversion (2)
Logic Family - Propagation Delay (H-L)
Logic Family - Propagation Delay (L-H)
Logic Family - Propagation Delay (3)
Bus Design Rules
Bus lines have very low line impedances (20 .. 40 Ohms).
• Bus lines have to be terminated to prevent line reflections
(signal distortion, circuit malfunctions due to undershoots).
• Take care of propagation times (25 ns/m). Settling time of
signals on TTL-type buses is 2 x tp (no incident wave
switching).
• Take care of control lines (clock, read, write, etc.).
• Provide shielding between control lines and data /
address lines.
Bus Design Rules
• A multiplexed data and address bus reduces design
problems (50% less signal lines and 50% less line driver).
• Driver output current is 100 mA/line. Provide adequate
and low inductance GND return path (simultaneous
switching)!
• Rule of thumb: 25% of all backplane connector pins have
to be GND lines!
• Use multilayer boards with separate GND and Vcc plane
for backplanes.
Acknowledgements
• I used Altium Protel 98 and Protel DXP to
create these schematic diagrams
• Logic Timing Diagrams are from Texas
Instruments (TI) Logic Selection Guide Digital Design Seminar
• National Semiconductor data sheets 74LS138.
• Motorola 11rm.pdf Reference Manual