Rainbow Electronics AT89C5122 - Manual (Page 48)

48
AT8xC5122/23
4202E–SCR–06/06
SCIB Clock The Smart Card Interface Block (SCIB) uses two clocks :
– The first one, CK_IDLE, is the peripheral clock used for the interface with the
microcontroller.
– The second one, CK_ISO, is independant from the CPU clock and is
generated from the PLL or XTAL1 output.
PR2, a 6-bit prescaler, will be used to generate:
12/9.6/8/6.85/6/5.33/4.8/4.36/ ..../1MHz frequencies.
SCIB clock frequency must be lower than CPU clock frequency.
During SCIB Reset, the CK_ISO input must be in the range 1 - 5 MHz according to ISO
7816. The SCIB clocks frequency is defined in Figure 42 on page 74 and Table 42 on
page 74.
Two conditions must be met for a correct use of the SCIB:
• CK_CPU > 4/3 * CK_ISO and
• CK_CPU < 6 * CK_ISO.
96 MHz
CPU frequency
24 MHz
PLL
1/4
Prescaler
48 MHz 1/2
External Clock CPU frequency
24 MHz
(Equivalent to)
X1 mode selected
24 MHz
CPU frequency
24 MHz
(Equivalent to)
X2 mode selected
PERIPH frequency
24 MHz
PERIPH frequency
24 MHz
PERIPH frequency
24 MHz
External Clock