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RD2 Kit - HW Description

RD2 Kit is a simple and cheap development Kit for quick development of new applications and learning the C language. The Kit contains a T89c51RD2 microcontroller and basic peripherals.

The Kit is programmed using the ISP programming method. There is a special program called loader in the RD2 micro, loaded in the internal program memory starting at the address FC00h. (This is the last 1kB of the internal program memory). The loader is started by jumping to the address FC00h if a special combination is set on the pins MOVC, ALE and PSEN is equal to 0. The programming mode is started by pulling the PSEN pin low and issuing a reset. The PC flasher communicates with the MCUs loader and it sends the entire 63kB of HEX code to the loader. The loader included in the RD2 Kit is fully compatible with the original one and it can also program the internal data EEPROM memory. .

Theres no need of a special programmer and a lot of cables on your desktop. You need only one PC, a RD2 Kit, power supply or adapter, a text editor and a C compiler with HEX output.


The micro T89c51RD2 is compatible with the standard 8051 family. There are some extensions:
  • 64 kB FLASH on chip memory which is programmable by ISP,
  • 2 kB EEPROM that sustains 100 000 writing cycles,
  • 1 kB internal RAM,
  • Software-selectable clock prescaler of 6 to 12 ticks by one cycle (X2 - Mode),
  • Max. frequency 20 Mhz (6 clocks/cycle) or 40 Mhz (12 clocks/cycle),
  • 7 interrupt sources in 4 priority levels
  • Power Down support,
  • Programmable clock output,
  • Program Counter Array PCA,
  • Second Data pointer DPTR,
  • Option to turn off ALE,
  • HW Watchdog.
For other details of T89c51RD2 see or the T89c51RD2 datasheet on the HW CD.

Basic parameters of the RD2 Kit

  • T89c51RD2 microcontroller in DIL package, Xtal 18,4352 MHz.
  • LED connected to P1.3
  • RS-232 interface with TTL/RS-232 converter.
  • Jumper for activating the ISP programming.
  • Power-on reset circuit + RESET button.
  • A voltage stabilizer (9-15 V, 200 mA).
  • 10-pin LCD connector for LCD display + LCDs contrast setting
  • 20-pin universal I/O connector with ports P1 and P3.
  • 40-pin expansion connector 1:1 for external RAM connectivity
  • Dimensions: 90 x 50 mm.
We have made the RD2 Kit for the DIL package of T89c51RD2 only so that you can substitute another type of the micro quite easily. You can program several MCUs with our Kit without a need for special package convertors. Remember that the RD2 Kit is designed for learning and developing new applications.

RD2 Kit Power Supply

You have to use an external power supply for the Kit. The output voltage must be between 9V and 15V. There is no need to use stabilized power supply but there is no overvoltage fuse in the Kit, so the maximum 15V is the limit! The + terminal is in the middle of the power connector. We have used the 78L05 stabilizer with filtering and blocking capacitors. The stabilized 5V is connected to all the Kit connectors. The maximum current provided by the Kit is 200mA.

The RD2 Kit consumes between 10-20mA. Additional current consumption depends on the external circuits connected to the ports. Be careful if you are connecting some external circuits to the microcontroller. The maximum load of the MCU is (10mA to Vcc and 1mA to GND). The power on is signalized by green LED.


The reset is issued by the integrated reset generator MAX810. The crystal Q1 and capacitors C1, C2 form an oscillator. The crystal is soldered directly to the board, but it can be exchanged easily if needed. There is no need of any HW changes when changing the crystal value but remember to change the constants in your program, especially the ones related to the RS-232 communication. The loader synchronizes with the MCU automatically.

Description of the Connector

Several connectors are used for communication with other external peripherals. Detailed description is clear from the circuit diagram of the Kit.

The LCD display connector

Connector "PFL10 - LCD display" is used for the LCD connection in 4-bit communication mode. The pins are connected as follows:

Connector PFL10 LCD display Description
1 GND 1 GND Ground
2 VCC 2 VCC Power supply +5 V
3 CT 3 V0 Contrast setting
4 P1.0 4 RS The Data/Instruction register setting
5 P1.1 5 RW Read/Write operation
6 P1.2 6 EN LCD activation (data valid)
7 P1.4 11 DB4 Data bit 4
8 P1.5 12 DB5 Data bit 5
9 P1.6 13 DB6 Data bit 6
10 P1.7 14 DB7 Data bit 7

The contrast is set using the R2 trimmer which is placed next to the reset button. Data bits DB0-DB3 are not connected.

PFL20 - I/O Connector

The ports P1 and P3 are connected to the "PFL20 I/O Connector". Some pins are connected with the LCD pins as shown in following table:

Connector PFL20


LCD displej

1 P1.0 T2 external input/output of T2 timer 4 RS
2 P1.1 T2EX T2 timer controll 5 RW
3 P1.2 ECI external clock for PCA 6 EN
4 P1.3 CEX0 PCA comparator register 0 - -
5 P1.4 CEX1 PCA comparator register 1 11 DB4
6 P1.5 CEX2 PCA comparator register 2 12 DB5
7 P1.6 CEX3 PCA comparator register 3 13 DB6
8 P1.7 CEX4 PCA comparator register 4 14 DB7
9 P2.0 RxD serial data input - -
10 P2.1 TxD serial data output - -
11 P2.2 /INT0 external interrupt input 0 - -
12 P2.3 /INT1 external interrupt input 1 - -
13 P2.4 T0 T0 input - -
14 P2.5 T1 T1 input - -
15 P2.6 /WR writing to external memory - -
16 P2.7 /RD reading from external memory - -
17 PSEN /PSEN reading the external program memory - -
18 RESET Reset - -
19 GND Ground pin - -
20 VCC Power supply +5 V - -

There is a red LED connected to the P1.3 output andcontrolled by our examples

Connector PFL40 - CPU connector

The "PFL40 - CPU connector" is connected directly to the MCU (1:1). All of the MCU pins are available here. It can be used for instance to connect the external XRAM memory.

Connector PFL 40 CPU connector
1 P1.0 11 P3.2 21 P2.0 31 /EA  
2 P1.1 12 P3.2 22 P2.1 32 P0.0  
3 P1.2 13 P3.3 23 P2.2 33 P0.1  
4 P1.3 14 P3.4 24 P2.3 34 P0.2  
5 P1.4 15 P3.5 25 P2.4 35 P0.3  
6 P1.5 16 P3.6 26 P2.5 36 P0.4  
7 P1.6 17 P3.7 27 P2.6 37 P0.5  
8 P1.7 18 P3.8 28 P2.7 38 P0.6  
9 RST 19 XTAL2 29 /PSEN 39 P0.7  
10 P3.0 20 XTAL1 30 ALE 40 VCC  

JMP3 - LOADER Jumper

This Jumper sets the Loader activation method. The Jumper is connected to the PSEN pin of the MCU which is tested after each reset and indicates whether the Loader should be activated (program starts at the last 1kB of Flash program memory) or not (program starts at the beginning of the Flash program memory). The loader is activated if the PSEN pin is connected to 0 (GND).

If the Jumper is in LDR (1-2) position, the PSEN pin is controlled through the MAX232 by the CTS signal from serial port of the PC. The PSEN pin is then controlled automatically from the Flasher program. .

If the Jumper is in STD (2-3) position, The PSEN pin is connected to GND. You have to disconnect the Jumper from this position after the programming ends to run the program inside the MCU..

If there is no Jumper in any position, the ISP programming method is never activated and the program starts at the address 0000h.

Connector RS-232 - Cannon9

The MCU communicates with the environment using the full duplex serial channel. The TTL/RS-232 layers are converted by the MAX232 circuit. There are two TTL/232 convertors and a 5V/±10 V charge pump in the MAX232 circuit.

Connector RS-232 CAN 9F (DB9) PC - cannon 9Male
2 TxD 2 RxD
3 RxD 3 TxD

Connector POWER - +5V

There are the +5V power supply and GND connected to this connector. Make sure that the connected peripherals do not exceed the maximum total current consumption of 200mA. .


T89c51RD2 is one of the latest MCUs based on x51 developed and presented by the Atmel company. It is not an ideal MCU, which does not exist but there are several features of this chip which can be very useful for the developers and which where suitable for designing the RD2 Kit. The RD2 Kit is suitable for beginners, students, teachers or real professionals.

Author: Jan Rehak

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