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4.4.2
Keypad
The Keypad has a 5 x 5 matrix, allowing 25 keys to be scanned. When a key being pressed, a keypad interrupt is generated.
To find which key has been pressed, the software scans each column in turn and reads which row is active. Because of key
bounce, the key press is confirmed twice at approximately 20 ms intervals.
U600
CALYPSO
U620
IOTA
10571-1
As the End Key doubles for the ON / OFF key, it is allocated an entire row of the keyboard scan.
Keyboard scanning is controlled by software. 'Key pressed' is indicated by an interrupt, but 'key released' is monitored by
software.
4.4.3
Subscriber Identity Module (SIM)
The SIM interface is designed to support 3 V SIMs. As CALYPSO operates from a 2.8 V supply, level translation from 3 V is
provided by IOTA.
MMCD020801C8
Service Manual
Figure 4.4: Keypad Connections
Section 4
– 11 –
TECHNICAL DESCRIPTION
Issue 1
Revision 0
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