dp83251 National Semiconductor Corporation, dp83251 Datasheet - Page 39

• Manufacturer Part Number: dp83251
• Description: Player Device Fddi Physical Layer Controller
• Manufacturer: National Semiconductor Corporation

5 0 Registers
NOISE PRESCALE THRESHOLD REGISTER (NPTR)
The Noise Prescale Threshold Register contains the start value for the Noise Prescale Counter The Noise Prescale Counter is a
count-down counter and it is used in conjunction with the Noise Counter for counting the Noise events The Noise Prescale
Counter decrements once every 80 ns while there is a noise event When the Noise Prescale Counter reaches zero it reloads
the count with the content of the Noise Prescale Threshold Register and also causes the Noise Counter to decrement
The threshold values for the Noise Counter and Noise Prescale Counter are simultaneously loaded into both counters if one of
the following conditions is true
(1) Both the Noise Counter and Noise Prescale Counter reach zero and the current Line State is either Noise Line State Active
or
(2) The current Line State is either Halt Line State Idle Line State Master Line State Quiet Line State or No Signal Detect
or
(3) The Noise Threshold Register or Noise Prescale Threshold Register goes through a Control Bus Interface write cycle
In addition the value of the Noise Prescale Threshold register is loaded into the Noise Prescale Counter if the Noise Prescale
Counter reaches zero
The Noise Counter and Noise Prescale Counter will continue to count without resetting or reloading the threshold values if a
Line State change occurs and the new line state is either Noise Line State Active Line State or Line State Unknown
When both the Noise Threshold Counter and Noise Counter both reach zero the Noise Threshold bit of the Receive Condition
Register A will be set
ACCESS RULES
D0
D1 – 6
D7
Line State or Line State Unknown
D7
NPT7
ADDRESS
Bit
0Eh
D6
NPT6
(Continued)
NPT0
NPT7
NPT1 – 6
Symbol
READ
Always
D5
NPT5
D4
NPT4
WRITE
Always
NOISE PRESCALE THRESHOLD BIT
start value of the Noise Prescale Counter
NOISE PRESCALE THRESHOLD BIT
value for the Noise Prescale Counter
NOISE PRESCALE THRESHOLD BIT
start value for the Noise Prescale Counter
D3
NPT3
39
D2
NPT2
Description
D1
NPT1
k
k
k
1 – 6
0
7
l
l
l
Least significant bit (LSB) of the
Most significant bit (MSB) of the
Intermediate bits of start
D0
NPT0