AT89C51CC01 Atmel Corporation, AT89C51CC01 Datasheet - Page 6
AT89C51CC01
Manufacturer Part Number
AT89C51CC01
Description
Manufacturer
Atmel Corporation
Datasheets
1.AT89C51CC01.pdf
(167 pages)
2.AT89C51CC01.pdf
(12 pages)
3.AT89C51CC01.pdf
(32 pages)
4.AT89C51CC01.pdf
(29 pages)
Specifications of AT89C51CC01
Flash (kbytes)
32 Kbytes
Max. Operating Frequency
40 MHz
Cpu
8051-12C
Max I/o Pins
34
Uart
1
Can
1
Adc Channels
8
Adc Resolution (bits)
10
Adc Speed (ksps)
62.5
Sram (kbytes)
1.25
Eeprom (bytes)
2048
Self Program Memory
API
Operating Voltage (vcc)
3.0 to 5.5
Timers
4
Isp
UART/CAN
Watchdog
Yes
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Quasi-Bidirectional Port
Operation
6
A/T89C51CC01
Table 1. Read-Modify-Write Instructions
It is not obvious the last three instructions in this list are Read-Modify-Write instructions.
These instructions read the port (all 8 bits), modify the specifically addressed bit and
write the new byte back to the latch. These Read-Modify-Write instructions are directed
to the latch rather than the pin in order to avoid possible misinterpretation of voltage
(and therefore, logic) levels at the pin. For example, a Port bit used to drive the base of
an external bipolar transistor can not rise above the transistor’s base-emitter junction
voltage (a value lower than VIL). With a logic one written to the bit, attempts by the CPU
to read the Port at the pin are misinterpreted as logic zero. A read of the latch rather
than the pins returns the correct logic-one value.
Port 1, Port 2, Port 3 and Port 4 have fixed internal pull-ups and are referred to as
"quasi-bidirectional" Ports. When configured as an input, the pin impedance appears as
logic one and sources current in response to an external logic zero condition. Port 0 is a
"true bidirectional" pin. The pins float when configured as input. Resets write logic one to
all Port latches. If logical zero is subsequently written to a Port latch, it can be returned
to input conditions by a logical one written to the latch.
Note:
Logical zero-to-one transitions in Port 1, Port 2, Port 3 and Port 4 use an additional pull-
up (p1) to aid this logic transition (see Figure 4.). This increases switch speed. This
extra pull-up sources 100 times normal internal circuit current during 2 oscillator clock
periods. The internal pull-ups are field-effect transistors rather than linear resistors. Pull-
ups consist of three p-channel FET (pFET) devices. A pFET is on when the gate senses
logical zero and off when the gate senses logical one. pFET #1 is turned on for two
oscillator periods immediately after a zero-to-one transition in the Port latch. A logical
one at the Port pin turns on pFET #3 (a weak pull-up) through the inverter. This inverter
and pFET pair form a latch to drive logical one. pFET #2 is a very weak pull-up switched
on whenever the associated nFET is switched off. This is traditional CMOS switch con-
vention. Current strengths are 1/10 that of pFET #3.
MOV Px.y, C
Instruction
CLR Px.y
SET Px.y
DJNZ
DEC
ANL
ORL
XRL
CPL
JBC
INC
Port latch values change near the end of Read-Modify-Write instruction cycles. Output
buffers (and therefore the pin state) update early in the instruction after Read-Modify-
Write instruction cycle.
Description
logical AND
logical OR
logical EX-OR
jump if bit = 1 and clear bit
complement bit
increment
decrement
decrement and jump if not zero
move carry bit to bit y of Port x
clear bit y of Port x
set bit y of Port x
Example
ANL P1, A
ORL P2, A
XRL P3, A
JBC P1.1, LABEL
CPL P3.0
INC P2
DEC P2
DJNZ P3, LABEL
MOV P1.5, C
CLR P2.4
SET P3.3
4129N–CAN–03/08