Rainbow Electronics AT89C51SND1C - Manual (Page 9)

9
AT8xC51SND1C
4109E–8051–06/03
Table 10. A/D Converter Signal Description
Table 11. Keypad Interface Signal Description
Table 12. External Access Signal Description
Signal
Name Type Description
Alternate
Function
AIN1:0 I A/D Converter Analog Inputs -
AREFP I Analog Positive Voltage Reference Input -
AREFN I
Analog Negative Voltage Reference Input
This pin is internally connected to AVSS.
-
Signal
Name Type Description
Alternate
Function
KIN3:0 I
Keypad Input Lines
Holding one of these pins high or low for 24 oscillator periods triggers a
keypad interrupt.
P1.3:0
Signal
Name Type Description
Alternate
Function
A15:8 I/O
Address Lines
Upper address lines for the external bus.
Multiplexed higher address and data lines for the IDE interface.
P2.7:0
AD7:0 I/O
Address/Data Lines
Multiplexed lower address and data lines for the external memory or the
IDE interface.
P0.7:0
ALE O
Address Latch Enable Output
ALE signals the start of an external bus cycle and indicates that valid
address information is available on lines A7:0. An external latch is used
to demultiplex the address from address/data bus.
-
ISP I/O
ISP Enable Input AT89C51SND1C Only
This signal must be held to GND through a pull-down resistor at the
falling reset to force execution of the internal bootloader.
-
RD O
Read Signal
Read signal asserted during external data memory read operation.
P3.7
WR O
Write Signal
Write signal asserted during external data memory write operation.
P3.6