ICS1893CFILF datasheet(45/126 Pages) ICST

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Chapter 7 Management Register Set

ICS1893CF, Rev. F, 03/01/07

Mar. 2007

ICS1893CF Data Sheet Rev. F - Release

7.1.4 Management Register Bit Special Functions

This section discusses the types of special functions for the Management Register bits.

7.1.4.1 Latching High Bits

The purpose of a latching high (LH) bit is to record an event. An LH bit records an event by monitoring an

active-high signal and then latching this active-high signal when it triggers (that is, when the event occurs).

A latching high bit, once set to logic one, remains set until either a reset occurs or it is read by an STA.

Immediately following an STA read of an LH bit, the ICS1893CF latches the current state of the signal into

the LH bit. When an STA reads an LH bit:

• Once, the LL bit provides the STA with a history of whether or not the event has ever occurred. That is,

this first read provides the STA with a history of the condition and latches the current state of the signal

into the LL bit for the next read.

• Twice in succession, the LH bit provides the STA with the current state of the monitored signal.

7.1.4.2 Latching Low Bits

As with latching high bits, the purpose of a latching low (LL) bit is also to record an event. An LL bit records

an event by monitoring an active-low signal and then latching this active-low signal when it triggers (that is,

when the event occurs).

A latching low bit, once cleared to logic zero, remains cleared until either a reset occurs or it is read by an

STA. Immediately following an STA read of an LL bit, the ICS1893CF latches the current state of the

active-low signal into the LL bit. When an STA reads an LL bit:

• Once, the LL bit provides the STA with a history of whether or not the event has ever occurred. That is,

this first read provides the STA with a history of the condition and latches the current state of the signal

into the LL bit for the next read.

• Twice in succession, the LL bit provides the STA with the current state of the monitored signal.

7.1.4.3 Latching Maximum Bits

For the ICS1893CF, the purpose of latching maximum (LMX) bits is to track the progress of internal state

machines. The LMX bits act in combination with other LMX bits to save the maximum collective value of a

defined group of LMX bits, from the most-significant bit to the least-significant bit.

For example, assume a group of LMX bits is defined as register bits 13 through 11. If these bits first have a

value of 3o (octal) and then the state machine they are monitoring advances to state:

• 2o, then the 2o value does not get latched.

• 4o (or any other value greater than 3o), then in this case, the value of 4o does get latched.

LMX bits retain their value until either a reset occurs or they are read by an STA. Immediately following an

STA read of a defined group of LMX bits, the ICS1893CF latches the current state of the monitored state

machine into the LMX bits. When an STA reads a group of LMX bits:

• Once, the LMX bits provide the STA with a history of the maximum value that the state machine has

achieved and latches the current state of the state machine into the LMX bits for the next read.

• Twice in succession, the LMX bits provide the STA with the current state of the monitored state machine.

7.1.4.4 Self-Clearing Bits

Self-clearing (SC) bits automatically clear themselves to logic zero after a pre-determined amount of time

without any further STA access. The SC bits have a default value of logic zero and are triggers to begin

execution of a function. When the STA writes a logic one to an SC bit, the ICS1893CF begins executing the

function assigned to that bit. After the ICS1893CF completes executing the function, it clears the bit to

indicate that the action is complete.

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