Specifications

48
3706C–MICRO–2/11
AT89LP3240/6440
10.2 Port Analog Functions
The AT89LP3240/6440 incorporates two analog comparators and an 8-channel analog-to-digital
converter. In order to give the best analog performance and minimize power consumption, pins
that are being used for analog functions must have both their digital outputs and digital inputs
disabled. Digital outputs are disabled b
y putting the port pins into the input-only mode as
described in “Port Configuration” on page 45. The analog input pins will always default to input-
only mode after reset regardless of the state of the Tristate-Port Fuse.
Digital inputs on P2.4, P2.5, P2.6 and P2.7 are disabled whenever an analog comparator is
enabled by setting the CENA or CENB bits in ACSRA and ACSRB and th
at pin is configured for
input-only mode. To use an analog input pin as a high-impedance digital input while a compara-
tor is enabled, that pin should be configured in open-drain mode and the corresponding port
register bit should be set to 1.
Digital inputs on Port 0 are disabled for each pin configured for input-only mode whenever the
ADC is enabled by s etting the ADCE bit and clearing the DAC
bit in DADC. To use any Port 0
input pin as a high-impedance digital input while the ADC is enabled, that pin should be config-
ured in open-drain mode and the corresponding port register bit should be set to 1. When DAC
mode is enabled, P2.2 and P2.3 are forced to input-only mode.
10.3 Port Read-Modify-Write
A read from a port will read either the state of the pins or the state of the port register depending
on which instruction is used. Simple read instructions will always access the port pins directly.
Read-modify-write instructions, which read a value, possibly modify it, and then write it back, will
always access the port register. This inclu des bit write instructions
such as CLR or SETB as they
actually read the entire port, modify a single bit, then write the data back to the entire port. See
Table 10-4 for a complete list of Read-Modify-Write instruction which may access the ports.
Table 10-4. Port Read-Modify-Write Instructions
Mnemonic Instruction Example
ANL Logical AND ANL P1, A
ORL Logical OR ORL P1, A
XRL Logical EX-OR XRL P1, A
JBC Jump if bit set and clear bit JBC P3.0, LABEL
CPL Complement bit CPL P3.1
INC Increment INC P1
DEC Decrement DEC P3
DJNZ Decrement and jump if not zero DJNZ P3, LABEL
MOV PX.Y, C Move carry to bit Y of Port X MOV P1.0, C
CLR PX.Y Clear bit Y of Port X CLR P1.1
SETB PX.Y Set bit Y of Port X SETB P3.2