Rainbow Electronics AT83C24NDS - Manual (Page 11)

11
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):
1. a clock for the CCLK: Four different sources can be used: CLK pin, DCCLK signal,
CARDCK bit or A2/CK pin (in transparent mode).
2. a clock for DC/DC converter.
CIO
0
1
0
1
CARDIO bit
CC4
CC8
0
1 CARDC8 bit
IODIS bit
CARDC4 bit
I/O
C4
C8
CVCC
CVCC
CVCC
EVCC
EVCC