DP83251 datasheet(43/96 Pages) NSC

43 / 96 page

50 Registers (Continued)

STATE PRESCALE THRESHOLD REGISTER (SPTR)

The State Prescale Threshold Register contains the start value for the State Prescale Counter The State Prescale Counter is a

down counter The Register is used in conjunction with the State Counter to count the Line State duration

The State Prescale Counter will decrement every 80 ns if the current Line State is Halt Line Idle Line State Master Line State

Quiet Line State or No Signal Detect As a result the State Prescale Counter takes SPTR x 80 ns to reach zero during a

continuous line state condition When the State Prescale Counter reaches zero the State Prescale Threshold Register will be

reloaded into the State Prescale Counter

The threshold values for the State Counter and State Prescale Counter are simultaneously loaded into both counters if one of

the following conditions is true

(1) Both the State Counter and State Prescale Counter reach zero and the current Line State is Halt Line State Idle Line State

Master Line State Quiet Line State or No Signal Detect

(2) A Line State change occurs and the new Line State is Halt Line State Idle Line State Master Line State Quiet Line State or

No Signal Detect

(3) The State Threshold Register or State Prescale Threshold Register goes through a Control Bus Interface write cycle

The State Counter and State Prescale Counter will reset by reloading the threshold values if a Line State change occurs and the

new Line State is Halt Line State Idle Line State Master Line State Quiet Line State or No Signal Detect

ACCESS RULES

ADDRESS

READ

WRITE

12h

Always

SPT7

SPT6

SPT5

SPT4

SPT3

SPT2

SPT1

SPT0

Bit

Symbol

Description

SPT0

STATE PRESCALE THRESHOLD BIT k0l

Least significant bit (LSB) of

the start value for the State Prescale Counter

D1–6

SPT1–6

STATE PRESCALE THRESHOLD BIT k1–6l

Intermediate bits of start

value for the State Prescale Counter

SPT7

STATE PRESCALE THRESHOLD BIT k7l

Most significant bit (MSB) of

the start value for the State Prescale Counter

DP83251 Datasheet(PDF) 43 Page - National Semiconductor (TI)

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