Cypress CY4672 manual Ghost Key Detection, Interrupt Usage / Timing

Keyboard

Example of a Battery Voltage Level report with fully charged batteries is shown in Table 4-18.

Table 4-18. Example ‘full’ Battery Voltage Level Report

	Application Report
Application	Battery Voltage Level
Report Header
0xFD	0x0A

Example of a Battery Voltage Level report with low batteries is shown in Table 4-19.

Table 4-19. Example ‘low’ Battery Voltage Level Report

Application Report

Application Report	Battery Voltage Level
Header
0xFD	0x01

4.3.10Ghost Key Detection

Ghost keys are possible on the RDK keyboard because it does not use diodes with the keyboard switches. Ghost keys are caused when three keys are pressed at the same time and two of the keys are on the same column and two of the keys are on the same row. When scanning the keyboard, it appears that four keys have been pressed and it is impossible to tell which three of the four keys are actually valid. The keyboard code detects this condition and does not send a report until one of the three keys is released.

For example, assume the keys (RowX, ColumnA), (RowX, ColumnB), and (RowY, ColumnA) have been pressed as shown in Figure 4-8. It appears that the key (RowY, ColumnB) has been pressed as well when it has not since the other keys electrically connect RowY to ColumnB.

Figure 4-8. Ghost Key Example

4.3.11Interrupt Usage / Timing

In the RDK keyboard, the following interrupts have been enabled:

■Row Port interrupt

■Bind button interrupt

When either of the above interrupts occurs, its ISR sets the flag.

70 CY4672 Reference Design Guide, Document # 001-16968 Revision **

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