82C54_05 Datasheet, PDF (15/22 Pages) Intersil Corporation – CMOS Programmable Intervel Timer

82C54
Counter will be loaded with new count on the next CLK pulse
and counting will continue from there.
CW = 1A LSB = 3
WR
CLK
GATE
OUT
NNN
NN
0
3
0
2
0
1
0 FF 0
0 FF 3
CW = 1A LSB = 3
WR
CLK
GATE
OUT
NN N NN
N
0
3
0
2
0
3
0
2
0 0 FF
1 0 FF
CW = 1A LSB = 3
WR
LSB = 5
CLK
GATE
OUT
N
N
N
N
N
0
3
00
21
0 FF FF ⁰
0 FF FE 5
0
4
FIGURE 14. MODE 5
Operation Common To All Modes
Programming
When a Control Word is written to a Counter, all Control
Logic, is immediately reset and OUT goes to a known initial
state; no CLK pulses are required for this.
Gate
The GATE input is always sampled on the rising edge of
CLK. In Modes 0, 2, 3 and 4 the GATE input is level
sensitive, and logic level is sampled on the rising edge of
CLK. In modes 1, 2, 3 and 5 the GATE input is rising-edge
sensitive. In these Modes, a rising edge of Gate (trigger)
sets an edge-sensitive flip-flop in the Counter. This flip-flop is
then sampled on the next rising edge of CLK. The flip-flop is
reset immediately after it is sampled. In this way, a trigger will
be detected no matter when it occurs - a high logic level
does not have to be maintained until the next rising edge of
CLK. Note that in Modes 2 and 3, the GATE input is both
edge-and level-sensitive.
Counter
New counts are loaded and Counters are decremented on
the falling edge of CLK.
The largest possible initial count is 0; this is equivalent to 2¹⁶
for binary counting and 10⁴ for BCD counting.
The counter does not stop when it reaches zero. In Modes 0,
1, 4, and 5 the Counter “wraps around” to the highest count,
either FFFF hex for binary counting or 9999 for BCD
counting, and continues counting. Modes 2 and 3 are
periodic; the Counter reloads itself with the initial count and
continues counting from there.
SIGNAL
STATUS
MODES
LOW OR
GOING LOW
RISING
HIGH
0 Disables Counting
-
Enables Counting
1
-
1) Initiates
-
Counting
2) Resets output
after next clock
2 1) Disables
Initiates Counting Enables Counting
counting
2) Sets output
immediately high
3 1) Disables
Initiates Counting Enables Counting
counting
2) Sets output
immediately high
4 1) Disables
Counting
-
Enables Counting
5
-
Initiates Counting
-
FIGURE 15. GATE PIN OPERATIONS SUMMARY
MODE
MIN COUNT
MAX COUNT
0
1
0
1
1
0
2
2
0
3
2
0
4
1
0
5
1
0
NOTE: 0 is equivalent to 2¹⁶ for binary counting and 10⁴ for BCD
counting.
FIGURE 16. MINIMUM AND MAXIMUM INITIAL COUNTS
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