HS1-82C54RH-8 Intersil, HS1-82C54RH-8 Datasheet - Page 9

• Manufacturer Part Number: HS1-82C54RH-8
• Manufacturer: Intersil

Specifications of HS1-82C54RH-8

• Lead Free Status / RoHS Status: Supplier Unconfirmed

A new initial count may be written to a Counter at any time
without affecting the Counter’s programmed Mode in
anyway. Counting will be affected as described in the Mode
definitions. The new count must follow the programmed
count format.
If a Counter is programmed to read/write two-byte counts,
the following precaution applies: A program must not
transfer control between writing the first and second byte to
another routine which also writes into that same Counter.
Otherwise, the Counter will be loaded with an incorrect
count.
Read Operations
It is often desirable to read the value of a Counter without
disturbing the count in progress. This is easily done in the
HS-82C54RH.
There are three possible methods for reading the Counters.
The first is through the Read-Back Command, which is
explained later. The second is a simple read operation of the
Counter, which is selected with the A1, A0 inputs. The only
requirement is that the CLK input of the selected Counter
must be inhibited by using either the GATE input or external
logic. Otherwise, the count may be in process of changing
when it is read, giving an undefined result.
Counter Latch Command
The other method for reading the Counters involves a
special software command called the “Counter Latch
Command”. Like a Control Word, this command is written to
the Control Word Register, which is selected when A1, A0 =
11. Also, like a Control Word, the SC0, SC1 bits select one
of the three Counters, but two other bits, D5 and D4,
distinguish this command from a Control Word.
A1, A0 = 11; CS = 0; RD = 1; WR = 0
The selected Counter’s Output Latch (OL) latches the count
when the Counter Latch Command is received. This count is
held in the latch until it is read by the CPU (or until the
Counter is reprogrammed). The count is then unlatched
automatically and the OL returns to “following” the Counting
Element (CE). This allows reading the contents of the
SC1, SC0 - specify counter to be latched
D5, D4 = 00 designates Counter Latch Command
X = Don’t Care
NOTE: Don’t Care bits (X) should be 0 to insure compatibility with
future products.
SC1
D7
FIGURE 11. COUNTER LATCH COMMAND FORMAT
SC1
0
0
1
1
SC0
D6
D5
0
SC1
0
0
1
1
D4
0
9
D3
X
Read-Back Command
D2
X
Counter
0
1
2
D1
X
D0
HS-82C54RH
X
Counters “on the fly” without affecting counting in progress.
Multiple Counter Latch Commands may be used to latch
more than one Counter. Each latched Counter’s OL holds its
count until read. Counter Latch Commands do not affect the
programmed Mode of the Counter in any way.
If a Counter is latched and then, some time later, latched
again before the count is read, the second Counter Latch
Command is ignored. The count read will be the count at the
time the first Counter Latch Command was issued.
With either method, the count must be read according to the
programmed format; specifically, if the Counter is
programmed for two byte counts, two bytes must be read.
The two bytes do not have to be read one right after the
other; read or write or programming operations of other
Counters may be inserted between them.
Another feature of the HS-82C54RH 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.
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 12. 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
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 single
command is functionally equivalent to several Counter Latch
D5: 0 = Latch count of selected Counters(s)
D4: 0 = Latch status of selected Counters(s)
D3: 1 = Select Counter 2
D2: 1 = Select Counter 1
D1: 1 = Select Counter 0
D0: Reserved for future expansion; Must be 0
1. Read least significant byte.
2. Write new least significant byte.
3. Read most significant byte.
4. Write new most significant byte.
D7
1
D6
FIGURE 12. READ-BACK COMMAND FORMAT
1
COUNT
D5
STATUS
D4
CNT 2 CNT 1 CNT 0
D3
D2
D1
D0
0