MD82C54/B Intersil, MD82C54/B Datasheet - Page 14

• Manufacturer Part Number: MD82C54/B
• Manufacturer: Intersil
• Type: Programmabler

Specifications of MD82C54/B

• # Internal Timers: 1
• Propagation Delay Time: 260ns
• Operating Supply Voltage (min): 4.5V
• Operating Supply Voltage (typ): 5V
• Operating Supply Voltage (max): 5.5V
• Package Type: CDIP
• High Level Output Current: -2.5mA
• Low Level Output Current: 2.5mA
• Pin Count: 24
• Operating Temp Range: -55C to 125C
• Operating Temperature Classification: Military
• Mounting: Through Hole
• Lead Free Status / RoHS Status: Not Compliant

Mode 3 Is Implemented As Follows
EVEN COUNTS - OUT is initially high. The initial count is
loaded on one CLK pulse and then is decremented by two
on succeeding CLK pulses. When the count expires, OUT
changes value and the Counter is reloaded with the initial
count. The above process is repeated indefinitely.
ODD COUNTS - OUT is initially high. The initial count is loaded
on one CLK pulse, decremented by one on the next CLK pulse,
and then decremented by two on succeeding CLK pulses.
When the count expires, OUT goes low and the Counter is
reloaded with the initial count. The count is decremented by
three on the next CLK pulse, and then by two on succeeding
CLK pulses. When the count expires, OUT goes high again and
the Counter is reloaded with the initial count. The above
process is repeated indefinitely. So for odd counts, OUT will be
high for (N + 1)/2 counts and low for (N - 1)/2 counts.
MODE 4: SOFTWARE TRIGGERED MODE
OUT will be initially high. When the initial count expires, OUT
will go low for one CLK pulse then go high again. The
counting sequence is “Triggered” by writing the initial count.
GATE = 1 enables counting; GATE = 0 disables counting.
GATE has no effect on OUT.
After writing a Control Word and initial count, the Counter will
be loaded on the next CLK pulse. This CLK pulse does not
decrement the count, so for an initial count of N, OUT does not
strobe low until N + 1 CLK pulses after the initial count is
written.
If a new count is written during counting, it will be loaded on
the next CLK pulse and counting will continue from the new
count. If a two-byte count is written, the following happens:
This allows the sequence to be “retriggered” by software. OUT
strobes low N + 1 CLK pulses after the new count of N is
written.
1. Writing the first byte has no effect on counting.
2. Writing the second byte allows the new count to be
loaded on the next CLK pulse.
14
82C54
MODE 5: HARDWARE TRIGGERED STROBE
(RETRIGGERABLE)
OUT will initially be high. Counting is triggered by a rising
edge of GATE. When the initial count has expired, OUT will
go low for one CLK pulse and then go high again.
After writing the Control Word and initial count, the counter
will not be loaded until the CLK pulse after a trigger. This
CLK pulse does not decrement the count, so for an initial
count of N, OUT does not strobe low until N + 1 CLK pulses
after trigger.
A trigger results in the Counter being loaded with the initial
count on the next CLK pulse. The counting sequence is
triggerable. OUT will not strobe low for N + 1 CLK pulses
after any trigger GATE has no effect on OUT.
If a new count is written during counting, the current counting
sequence will not be affected. If a trigger occurs after the
new count is written but before the current count expires, the
GATE
GATE
GATE
OUT
CLK
OUT
OUT
CLK
CLK
WR
WR
WR
CW = 18
CW = 18
CW = 18
N
N
N
N
N
N
LSB = 3
LSB = 3
LSB = 3
N
N
N
FIGURE 13. MODE 4
N
N
N
0
3
0
3
0
3
LSB = 2
0
2
0
3
0
2
0
1
0
3
0
1
0
2
0
2
0
0
0
1
FF
FF
0
1
0
0
FF
FE
0
0
FF
FF
FF
FF
FF
FD