27963 Parallax Inc, 27963 Datasheet - Page 9

• Manufacturer Part Number: 27963
• Description: SOLUTIONS CUBED: MEMKEY
• Manufacturer: Parallax Inc

Specifications of 27963

• Accessory Type: Keypad Encoder
• Product: Microcontroller Accessories
• For Use With/related Products: BASIC Stamp®
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Miniature Engineering Modules – MEMKey
Ghost Key Protection
rectangle in relation to the row and column assignment. In this case the fourth corner of the rectangle will also be read
as down.
be registered at one time. If more than 2 keys are pressed simultaneously, then no keys are registered as pressed.
This ensures that no ghost key is decoded as pressed. Because of this method, system designers must ensure that
three-key combinations are not implemented with the MEMKey, because the MEMKey will disallow any three-key
combinations.
SOLUTIONS CUBED
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Command Set and Communication Examples
A ghost key situation can arise when three keys are pressed simultaneously and they form the vertices of a
Read Key Buffer: No keys have been pressed
Automatic mode, default setup, keys 0, 4, 5 pressed one right after another
Program rows and columns: K0 = R0, K1 = R1, K2 = R2, K3 = R3, K4 = R4, K5 = C0, K6 = C1, K7 = C2, K8 = C3
Program user EEPROM address '35'H with 'AA'H and then read user EEPROM
Program key 16 to return PC/AT key value 'ENTER' then read key 16 PC/AT value
Setup MEMKey to have typematic mode and automatic key presses
'06'H
'08'H
'0D'
'0E'H
The MEMKey combats this situation by implementing a simple key counter and allowing no more than 2 keys to
'00'H
'00'H
'00'H
'35'H
'10'H
'06'H
'01'H
'AA'H
'33'H
'FF'H
'04'H
10mS for EEPROM write
10mS for EEPROM write
'02'H
address '35'H
'03'H
'09'H
'0D'H
'05'H
'04'H
'35'H
'16'H
'05'H
'AA'H
'33'H
'06'H
'07'H
'08'H
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