CS5535-UDCF AMD (ADVANCED MICRO DEVICES), CS5535-UDCF Datasheet - Page 110

• Manufacturer Part Number: CS5535-UDCF
• Manufacturer: AMD (ADVANCED MICRO DEVICES)

Specifications of CS5535-UDCF

• Operating Temperature (min): 0C
• Operating Temperature (max): 85C
• Operating Temperature Classification: Commercial
• Mounting: Surface Mount
• Lead Free Status / RoHS Status: Compliant

The read-back command present in the 8254 PIT is used
to determine the current counter value and its status like
counting format, the counting mode, the low-order or high-
order byte or both being read or written, and the status of
its output. Figure 5-16 shows the format of the read-back
command. The two most significant bits define the read-
back command with their value 11b. CT and ST indicate
that the value and the status of the counter are to be deter-
mined respectively. The C0-C2 bits define the counter
whose value or status is to be determined. With the read-
back command, several counter latch commands can be
issued in parallel by indicating several counters simulta-
neously with the C0-C2 bits. The 8254 then behaves as if
several counter latch commands have been issued individ-
ually, and transfers the individual count values into the out-
put latches of each counter. All successive counter latch
110
31506B
CT: Determine count value of selected counter.
ST: Determine status of selected counter.
C2, C1, C0: Counter selection.
PIN: Status of counter output pin:
LOAD: Is counter loaded with a start value?
LH: Corresponds to bits [5:4] of the Control Word register.
MODE: Corresponds to bits [3:1] of the Control Word register.
BCD: Corresponds to bit 0 of the Control Word register.
PIN
7
1
7
0 = Determine count value.
1 = Do not determine count value.
0 = Determine count status.
1 = Do not determine count status.
0 = Counter not selected.
1 = Counter selected.
0 = Output pin low.
1 = Output pin high.
0 = Counter loaded, count value can be read.
1 = Counter not yet loaded, count value cannot be read.
LOAD
Figure 5-16. PIT Read-Back Command Format
6
1
6
Figure 5-17. PIT Status Byte Format
CT
5
5
LH
ST
4
4
C2
3
3
commands, whether issued by its own counter or a next
read-back command, are ignored if the counter concerned
has not been read by counter read instructions. To deter-
mine the programmed mode of a particular counter, set CT
= 1 and ST = 0.
The read-back command latches the current mode and
provides a status byte (see Figure 5-17) at the port address
of the counter concerned. This status byte is fetched by a
counter read instruction. The PIN bit indicates the current
status of the concerned counter’s output pin. If PIN = 1,
then the counter output is at logic 1, else at logic 0. Bit 0
shows whether the last written counter value has already
been transferred to the counter. Not before zero = 0 is it
meaningful to read back the counter value.
MODE
C1
2
2
AMD Geode™ CS5535 Companion Device Data Book
C0
1
1
BCD
0
x
0
Programmable Interval Timer