PSD511B1 datasheet(151/153 Pages) STMICROELECTRONICS

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PSD5XX Family

148

21.0

Process

Change Notice,

October 1, 1998

PSD5XX Functional Change:

A change has been implemented in the most recent silicon that improves the way that the

Image Register is updated. This change only applies to Event Count Mode for counter units

CTU0, CTU1, and CTU3.

Previous PSD5XX Silicon:

The Image Register was not updated with the actual event count upon exiting Freeze

mode. As a result, in certain circumstances, the Image Register may not have reflected the

actual event count. Although an incorrect count may have been read from the Image

eventually read the correct value in the Image Register on subsequent freeze and read

cycles.

Current PSD5XX Silicon:

The Image register is now automatically updated with the actual count upon exiting the

Freeze mode. This ensures that on the very next freeze and read cycle, the microcontroller

will read the actual count from the Image register. There are two restrictions however:

1. If an event occurs within one timer clock period plus two CLKIN periods after the image

freeze and read cycle (timer clock period is defined on page 6-79 of the 1996 PSD data

book). Instead, the event will appear in the Image Register on the subsequent freeze

and read cycle.

2. The time between an unfreeze and the beginning of the next freeze has the same time

constraint as number one. There must be at least one timer clock period plus two CLKIN

periods between the end of one freeze cycle and the beginning of the next. This timing

can be controlled by software design.

To reduce the chance of getting a delayed count in the Image Register due to restriction

number 1, execute a software Load/Store command just prior to freezing and reading the

Image Register to force an update to the Image count.

Backwards Compatibility:

This improvement should have no impact on current designs unless these designs

were compensating for lost events. In such cases, compatibility is dependent on the

compensation method that was used. Please contact WSI at apphelp@wsiusa.com if you

think you have an issue or have any questions.

PSD511B1 Datasheet(PDF) 151 Page - STMicroelectronics