MR82C54/B Intersil, MR82C54/B Datasheet - Page 7

• Manufacturer Part Number: MR82C54/B
• Manufacturer: Intersil
• Type: Programmabler

Specifications of MR82C54/B

• # Internal Timers: Single
• Propagation Delay Time: 260ns
• Operating Supply Voltage (min): 4.5V
• Operating Supply Voltage (typ): 5V
• Operating Supply Voltage (max): 5.5V
• Package Type: CLCC
• High Level Output Current: -2.5mA
• Low Level Output Current: 2.5mA
• Pin Count: 28
• Operating Temp Range: -55C to 125C
• Operating Temperature Classification: Military
• Mounting: Surface Mount
• Lead Free Status / RoHS Status: Not Compliant

read or write or programming operations of other Counters
may be inserted between them.
Another feature of the 82C54 is that reads and writes of the
same Counter may be interleaved; for example, if the
Counter is programmed for two byte counts, the following
sequence is valid.
1. Read least significant byte.
2. Write new least significant byte.
3. Read most significant byte.
4. Write new most significant byte.
If a counter is programmed to read or write two-byte counts,
the following precaution applies: A program MUST NOT
transfer control between reading the first and second byte to
another routine which also reads from that same Counter.
Otherwise, an incorrect count will be read.
Read-Back Command
The read-back command allows the user to check the count
value, programmed Mode, and current state of the OUT pin
and Null Count flag of the selected counter(s).
The command is written into the Control Word Register and
has the format shown in Figure 5. The command applies to
the counters selected by setting their corresponding bits D3,
D2, D1 = 1.
A0, A1 = 11; CS = 0; RD = 1; WR = 0
D5: 0 = Latch count of selected Counter (s)
D4: 0 = Latch status of selected Counter(s)
D3: 1 = Select Counter 2
D2: 1 = Select Counter 1
D1: 1 = Select Counter 0
D0: Reserved for future expansion; Must be 0
D7
1
D6
1
FIGURE 5. READ-BACK COMMAND FORMAT
COUNT
D5
STATUS
D4
CNT 2 CNT 1 CNT 0
D3
D2
D1
D0
0
82C54
7
The read-back command may be used to latch multiple
counter output latches (OL) by setting the COUNT bit D5 = 0
and selecting the desired counter(s). This signal command is
functionally equivalent to several counter latch commands,
one for each counter latched. Each counter’s latched count
is held until it is read (or the counter is reprogrammed). That
counter is automatically unlatched when read, but other
counters remain latched until they are read. If multiple count
read-back commands are issued to the same counter with-
out reading the count, all but the first are ignored; i.e., the
count which will be read is the count at the time the first
read-back command was issued.
The read-back command may also be used to latch status
information of selected counter(s) by setting STATUS bit D4
= 0. Status must be latched to be read; status of a counter is
accessed by a read from that counter.
The counter status format is shown in Figure 6. Bits D5
through D0 contain the counter’s programmed Mode exactly
as written in the last Mode Control Word. OUTPUT bit D7
contains the current state of the OUT pin. This allows the
user to monitor the counter’s output via software, possibly
eliminating some hardware from a system.