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參數(shù)資料
| 型號(hào)： | T89C51RC2-SLTCM |
| 廠商： | Atmel Corp. |
| 英文描述： | 8-bit Microcontroller with 16 Kbytes/ 32 Kbytes FLASH |
| 中文描述： | 8位微控制器，帶有16字節(jié)/ 32千字節(jié)閃存 |
| 文件頁(yè)數(shù)： | 10/170頁(yè) |
| 文件大?。?/td> | 1927K |
| 代理商： | T89C51RC2-SLTCM |
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10
A/T89C51CC01
4129L–CAN–08/05
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.
Quasi-Bidirectional Port
Operation
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:
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.
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.
Figure 4.
Internal Pull-Up Configurations
Note:
Port 2 p1 assists the logic-one output for memory bus cycles.
READ PIN
INPUT DATA
P1.x
P2.x
P3.x
P4.x
OUTPUT DATA
2 Osc. PERIODS
n
p1(1)
p2
p3
VCC
VCC
VCC
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| T89C51RC2-SLTIM | 8-bit Microcontroller with 16 Kbytes/ 32 Kbytes FLASH |
| T89C51RD2 | 0 to 40MHz Flash Programmable 8-bit Microcontroller |
| T89C51RD2-3CBC-L | 0 to 40MHz Flash Programmable 8-bit Microcontroller |
| T89C51RD2-3CBC-M | 0 to 40MHz Flash Programmable 8-bit Microcontroller |
| T89C51RD2-DDBC-L | 0 to 40MHz Flash Programmable 8-bit Microcontroller |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| T89C51RC2-SLTIL | 制造商:ATMEL 制造商全稱:ATMEL Corporation 功能描述:8-bit Microcontroller with 16 Kbytes/ 32 Kbytes FLASH |
| T89C51RC2-SLTIM | 制造商:ATMEL 制造商全稱:ATMEL Corporation 功能描述:8-bit Microcontroller with 16 Kbytes/ 32 Kbytes FLASH |
| T89C51RC2-SLWCL | 制造商:ATMEL 制造商全稱:ATMEL Corporation 功能描述:8-bit Microcontroller with 16 Kbytes/ 32 Kbytes FLASH |
| T89C51RC2-SLWCM | 制造商:ATMEL 制造商全稱:ATMEL Corporation 功能描述:8-bit Microcontroller with 16 Kbytes/ 32 Kbytes FLASH |
| T89C51RC2-SLWIL | 制造商:ATMEL 制造商全稱:ATMEL Corporation 功能描述:8-bit Microcontroller with 16 Kbytes/ 32 Kbytes FLASH |
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