Chapter 1. Introduction
STC90C51RC/RD+ series, which is produced by STC MCU Limited, is a 8-bit single-chip microcontroller
with a fully compatible instruction set with industrial-standard 8051 series microcontroller. There is 64K bytes
flash memory embeded for appliaction program, which is shared with In-System-Programming code.In-System-
Programming (ISP) and In-Application-Programming (IAP) support the users to upgrade the program and data
in system. ISP allows the user to download new code without removing the microcontroller from the actual end
product; IAP means that the device can write non-valatile data in Flash memory while the application program
is running. There are 1280 bytes or 512 bytes on-chip RAM embedded that provides requirement from wide
field application. The user can configure the device to run in 12 clocks per machine cycle, and to get the same
performance just as he uses another standard 80C51 device that is provided by other vendor, or 6 clocks per
machine cycle to achieve twice performance. The STC90C51RC/RD+ series retain all features of the standard
80C51. In addition, the STC90xx series have a extra I/O port (P4 ), Timer 2, a 8-sources, 4-priority-level interrupt
structure, on-chip crystal oscillator,and a one-time enabled Watchdog Timer.
1.1 Features
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Enhanced 80C51 Central Processing Unit ,6T or 12T per machine cycle
Operation voltage range: 5.5V~3.3V (STC90C51RC/RD+ series) or 2.0V~ 3.6V (STC90LE51RC/RD+ series)
Operation frequency range: 0-40MHz @ 6T, or 0- 80MHz @12T, the actual operation frequency can up to
48MHz
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On-chip 4K/8K/13K/16K/32K/40K/48K/56K/61K FLASH program memory with flexible ISP/IAP capability
On-chip 1280 byte / 512 byte / 256 byte RAM
Be capable of addressing up to 64K byte of external RAM
Be capable of addressing up to 64K bytes external memory
Dual Data Pointer (DPTR) to speed up data movement
Three 16-bit timer/counter, Timer 2 is an up/down counter with programmable clcok output on P1.0
8 vector-address, 4 level priority interrupt capability
One enhanced UART with hardware address-recognition, frame-error detection function, and with self baud-
rate generator.
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One 15 bits Watch-Dog-Timer with 8-bit pre-scaler (one-time-enabled)
integrate MAX810 — specialized reset circuit
Two power management modes: idle mode and power-down mode
Low EMI: inhibit ALE emission
Power down mode can be woken-up by INT0/P3.2 pin, INT1/P3.3 pin, T0/P3.4, T1/P3.5, RXD/P3.0 pin,
INT2/P4.3, INT3/P4.2
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39 or 35 programmable I/O ports are available
Four 8-bit bi-directonal ports; extra four-bit additional P4 are available for PLCC-44 and LQFP-44
Operating temperature: -40 ~ +85oC (industrial) / 0~75oC (commercial)
package type : LQFP-44, PDIP-40, PLCC-44
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STC MCU Limited.