AT83C24B datasheet(11/42 Pages) ATMEL

11 / 42 page

4234F–SCR–10/05

AT83C24

CIO, CC4, CC8 Controller

The CIO, CC4, CC8 output pins are driven respectively by CARDIO, CARDC4, CARDC8 bits

values or by I/O, C4, C8 signal pins. This selection depends of the IODIS bit value. If IODIS is

reset, data are bidirectional between respectively I/O, C4, C8 pins and CIO, CC4, CC8 pins.

Figure 5. CIO, CC4, CC8 Block Diagram

IO and CIO pins are linked together through the on chip level shifters if IODIS bit=0 in INTER-

FACE register. This is done automatically during an hardware activation.

Their iddle level are 1. With IO high, CIO is pulled up.

The same behavior is applicable on C4/ CC4 and C8/ CC8 pins.

The maximum frequency on those lines depends on CLK frequency (3 clock rising edges to

transfer). With CLK=27MHz, the maximum frequency on this line is 1.5MHz.

Due to the minimum transfer delay allowed for NDS applications, the CLK minimum frequency is

18MHz.

Clock Controller

The clock controller generates two clocks (as shown in Figure 6 and Figure 7):

a clock for the CCLK: Four different sources can be used: CLK pin, DCCLK signal,

CARDCK bit or A2/CK pin (in transparent mode).

a clock for DC/DC converter.

CIO

CARDIO bit

CC4

CC8

CARDC8 bit

IODIS bit

CARDC4 bit

I/O

CVCC

EVCC

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