Real Time Operating Systems Application Board Details

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Peter Greene
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1 Real Time Operating Systems Application Board Details Hardware Interface All labs involve writing a C program to generate an interface between a PC and an external Multi-Applications board. A 40-way ribbon connector connects the PC to the Multi-Applications Board. A Digital Input/Output board containing an 82C55 PPI (Programmable Peripheral Interface) provides the interface on the PC side. Multi- Applications Board 2.1 Digital Input/Output Board The Digital Input/Output board sits in the PC ISA bus at base address 280H. The 82C55 PPI provides 2 8bit interfaces to the applications board. PORT B drives the output circuitry on the applications board (e.g. LEDs, seven segment display, motor, DAC). PORT C provides an 8 bit input from the applications board input circuitry (e.g. switches, ADC). A detailed description of programming the 82C55 is given in appendix 1. The 82C54 PIT provides timing waveforms via OUT1 to the applications board. OUT1 is used in the variable speed motor program. A detailed description of programming the 82C53 is given in appendix 2. Device 82C54 Counter 0 82C54 Counter 1 82C54 Counter 2 82C54 Control Word Register 82C55 Port A 82C55 Port B 82C55 Port C 82C55 Control Word Register Address 280H 281H 282H 283H 284H 285H 286H 287H Table 1:- Digital Input/Output Board Addresses 1

2 PC System Bus PORT A Control Register PORT B PORT C 82C55 PPI To Applications Board CNTR 0 Control Register CNTR 1 CNTR 2 OUT1 82C54 PIT Digital Input/Output Board 2

3 Multi-Applications Board The Multi-Applications board is a tool which has been developed to aid in the teaching of computer interfacing. The unit is a standalone board which connects to a PC via a 40 way ribbon cable. The board contains the following design units:- Switch inputs LED display Analog to Digital Converter (ADC) Digital to Analog Converter Keypad DC Motor Temperature sensor Seven Segment Display Applications Board Input Circuits Temp Sensor SW5 Motor Speed Sensor CK0 Strain Guage PC0 POT ADC To PC PC7 EXT Buffer PB0 PB1 PB2 PB * 0 # Switches 3

4 Applications Board Output Circuits LEDs Buffer Analog Out From PC PB7 PB0 DAC SW3.1 X Bar Graph PO Buffer X SW3.3 SW3.2 X Heat DC Motor SW3.4 X Buzzer Stepper Motor C Programs X SW3.4 4

5 This section provides the background information required to write each of the 7 C programs. Before testing your program ensure that the switch setting on the applications board correspond with Appendix 3. The C program template is shown below:- /*C program template*/ /*include required header libraries*/ #include <stdio.h> #include <conio.h> /*define addresses for 82C55 PPI*/ #define PORTA 0x284 #define PORTB 0x285 /*output port*/ #define PORTC 0x286 /*input port*/ #define CONTROL 0x287 void main() { /*variable definitions*/ /*configure PPI*/ outportb (CONTROL, 0x89); /*PortC is input, PortB is output*/ /*place code here*/ } To write a byte of data to the output circuitry of the applications board:- outportb(portb,ox54); /*writes 54H to PORT B of PPI*/ To read a byte of data from the input circuitry of the applications board:- unsigned char a; a = inport(portc); /*byte of data read from PORTC assigned to a*/ 5

6 Read applications board switch status. This program reads the status of octal switch SW1 on the applications board. The switch status should be displayed on the PC and also written to the applications board LEDs. PPI Applications Board Control Register PORT A PORT B LEDs PORT C SW1 6

7 Seven Segment Display The applications board contains a dual common-cathode seven segment display. 2 BCD to seven segment decoders are used to drive the displays. When the LE pin of a 4511 decoder is low the display shows the current BCD input. When the LE pin is high the 4511 outputs are frozen and a change on the BCD inputs will not be updated onto the display. Port B bits 1 to 4 are used to supply the BCD digit to the 4511 decoders. Port B bit 0 is used to drive the LE pins of the 4511 s. Right Display Left Display a b c d e f g 4511 D C B A LE a b c d e f g 4511 D C B A LE PB4 PB3 PB2 PB1 PB0 7

8 Display PB4 PB3 PB2 PB1 PB0 Port B H H H H H BH DH FH H H Codes to count from 0 to 9 on the right-hand display. Flowchart:- (0 to 9 count) i = 0 Output i th display value to Port B Increment i Y i = 10? N 8

9 Keypad Interface The applications board contains a 4x3 keypad. The keypad row inputs are connected to Port B of the PPI. The column outputs are connected to Port C. The column pins are pulled high to 5V. When a key a key is pressed the column pin is shorted to the corresponding row pin. To scan the keypad a 0 is applied to one row and the column pins are checked for non- 1 values. If the column pins are 111 then no key has been pressed. e.g. if Port B = FDH ( B) we are scanning row 2 If Port C = DFH ( B) the key pressed is 5. 5V * 0 # PB0 PB1 PB2 PB4 PC6 PC5 PC4 9

MEMORY-MAPPED I /O. Universiti Teknikal Malaysia Melaka. Input/Output System Design

MEMORY-MAPPED I /O. Universiti Teknikal Malaysia Melaka. Input/Output System Design Universiti Teknikal Malaysia Melaka Faculty of Electronics and Computer Engineering Department of Computer Engineering BENM 2123 MICROPROCESSOR TECHNOLOGY Instead of connecting to auxiliary memory, address