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BASEBAND OVERVIEW
Issue A
Section 6
MCUK990801G8
Revision 0
– 26 –
Technical Guide
6.2.1 Keypad
The Keypad has a 5 x 5 matrix in rows and columns, allowing 25 keys to be scanned. Each row has a built-in pull-up resistor
and the column line outputs are selected low. On a key press, the row input is pulled low by the corresponding column
generating a keypad interrupt. To ascertain which key has been pressed, the software asserts all columns high then takes each
one low. While each column is held low the rows are polled to see which one has been pulled low.
As the END key doubles as ON / OFF key, it is allocated an entire row of the keyboard scan.
To eliminate false key presses, i.e. key bounce, the key has to remain pressed for a minimum of 20 ms.
Keyboard scanning is software controlled. Key pressed is indicated by an interrupt, but key release is controlled by software.
Figure 6.2: Keypad Matrix
6.2.2 Subscriber Identity Module (SIM)
The SIM interface is designed to support 3 V and 5 V SIMs.
The GD90 GEMINI process is unable to support 5 V tolerant inputs. Therefore, in order to Interface GEMINI with a 2.8 V supply,
and the SIM with a 5 V supply, it is necessary to include a level shift. U505 is able to perform the required level shift. In addition
the device includes a switched capacitor charge pump DC/DC converter to generate the 5 V SIM supply from D2V8.
The SIM is initially activated by U505 with a 3 V supply and checks Status identification after receiving an ATR command. If
U505 detects a 3 V technology SIM, it operates it at 3 V. If a 5 V SIM, operation is switched to 5 V. If a faulty ATR is received
at 3 V, an error handling procedure is initiated. If the error handling does not result in an errorless ATR, the SIM is activated at
5 V. If no ATR is received at 3 V, the SIM will be deactivated and re-actived at 5 V.
4
3
D722
VOICE_MEMO
*
S701
7
S706
TP757
TP762
TP763
2
4
S711
TP764
1
0
1
S716
TP765
TP766
D729
PWR/END
0
0
S702
8
S707
TP758
5
S712
2
S417
1
#
S703
9
S708
TP759
6
S413
3
S718
2
OK
S704
<
S709
TP760
v
S714
SND
S719
3
CLR
S705
S721
nPOWKEY
>
S710
TP761
TP767
v
S715
PB
S720
4
3
12
4
KBC(0:4)
KBR(0:4)
10067-1
