DP83261AVF datasheet(57/132 Pages) NSC

57 / 132 page

60 Control Information (Continued)

66 TIMER VALUES

The Ring Engine stores several timer values and thresholds used in normal operation With the exception of TNEG the timers

use an exponential expansion on a 4-bit value to produce a negative twos complement 24-bit value used by the Timer Logic

The timer values are always readable and are writable in Stop Mode

Asynchronous Priority Threshold (THSH1)

The Ring Engine currently supports one Asynchronous Priority Threshold (THSH1) in addition to the one at TTRT The Asyn-

chronous Priority Threshold is used in a magnitude comparison with THT when an Asynchronous Priority Request is presented

to the MAC Request Interface

Bits 7 – 4 are always written to Zero and are always read as Zero

When more than one threshold is used the users of THSH1 have the lowest priority All asynchronous transmissions are limited

by TTRT If the Late Flag is set no frames may be transmitted regardless of the value of the Asynchronous Priority Threshold

ACCESS RULES

Address

Read

Write

87h

Always

Stop Mode

THSH1

Zero

THSH(3)

THSH(2)

THSH(1)

THSH(0)

Time remaining in THT

THSH1(3 – 0)

when token becomes unusable

1024 ms

2048 ms

4096 ms

8192 ms

16384 ms

32768 ms

65536 ms

13107 ms

26214 ms

52429 ms

10486 ms

20972 ms

41943 ms (default)

83886 ms

16777 ms

33554 ms

Warning

The default value may not be appropriate for all values of TNEG

In some cases this could result in a request that is NEVER serviced

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