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參數(shù)資料
| 型號： | TN87C54-20 |
| 廠商： | INTEL CORP |
| 元件分類： | 微控制器/微處理器 |
| 英文描述： | CHMOS SINGLE-CHIP 8-BIT MICROCONTROLLER WITH 16 KBYTES USER PROGRAMMABLE EPROM |
| 中文描述： | 8-BIT, OTPROM, 20 MHz, MICROCONTROLLER, PQCC44 |
| 封裝： | PLASTIC, LCC-44 |
| 文件頁數(shù)： | 7/20頁 |
| 文件大?。?/td> | 290K |
| 代理商： | TN87C54-20 |
AUTOMOTIVE 87C54/87C54-20
ONCE MODE
The ONCE (‘‘On-Circuit Emulation’’) Mode facilitates
testing and debugging of systems using the 87C54
without the 87C54 having to be removed from the
circuit. The ONCE Mode is invoked by:
1) Pull ALE low while the device is in reset and
PSEN is high;
2) Hold ALE low as RST is deactivated.
While the device is in ONCE Mode, the Port 0 pins
float and the other port pins and ALE and PSEN are
weakly pulled high. The oscillator circuit remains ac-
tive. While the 87C54 is in this mode, an emulator or
test CPU can be used to drive the circuit. Normal
operation is restored when a normal reset is applied.
RFI REDUCTION MODE
The RFI reduction feature can be used only if exter-
nal program memory is not required since this mode
disables the ALE pin during instruction code fetches.
By writing a logical one to the LSB of the Auxiliary
Register (address 08EH), the ALE is disabled for in-
struction code fetches and the output is weakly held
high. When a logical zero is written, the ALE pin is
enabled allowing it to generate the Address Latch
Enable signal. This bit is cleared by reset. Once dis-
abled, ALE remains disabled until it is reset by soft-
ware or until a hardware reset occurs.
Table 2. Status of the External Pins during Idle and Power Down
Mode
Program
Memory
ALE
PSEN
PORT0
PORT1
PORT2
PORT3
Idle
Internal
1
1
Data
Data
Data
Data
Idle
External
1
1
Float
Data
Address
Data
Power Down
Internal
0
0
Data
Data
Data
Data
Power Down
External
0
0
Float
Data
Data
Data
NOTE:
For more detailed information on the reduced power modes refer to current Embedded Applications Handbook, and Applica-
tion Note AP-252, ‘‘Designing with the 80C51BH.’’
7
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