Additional features, Clock, Card presence input – Rainbow Electronics AT89C5122 User Manual
Page 74
74
AT8xC5122/23
4202E–SCR–06/06
Additional Features
Clock
The CK_ISO input must be in the range 1 - 5 MHz according to ISO 7816.
The CK_ISO can be programmed up to 12 MHz. In this case, the timing specification of
the output buffer will not comply to ISO 7816.
Figure 41. Clock Diagram of the SCIB Block
Figure 42. Prescaler 2 Description
The division factor SCICLK must be smaller than 49. If it is greater or equal to 49, the
PR2 prescaler is locked.
See Figure 17 clock tree diagram in the clock controller chapter.
Table 42. Examples of Clock settings
Card Presence Input
The internal pull-up (weak pull-up) on Card Presence input can be disconnected in order
to reduce the consumption (CPRESRES, bit 3 in PMOD0).
In this case, an external resistor (typically 1 M
Ω
) must be externally tied to Vcc.
CPRES input can generate an interrupt (see Interrupt system section).
The detection level can be selected.
PR2
Ck_cpu
Ck_ISO
SCIB
CK_PLL or
CK_IDLE
CK_XTAL1
PR2
1/(2*(48 - SCICLK[5-0]))
CK_ISO
EXT48
PLLCON.2
0
1
CK_PLL
CK_XTAL1
XTSCS
SCICLK.7
SCICLK[5:0]
<48
=48
XTAL1 (MHz)
EXT48
SCICLK
CK_ ISO
8
0
36
4
8
0
44
12
8
0
42
8
8
0
40
6
8
0
24
2
8
0
0
1