1. ACCEL SOFTWARE AND TECHNOLOGIES LTD.
Day 02
Vdu Basics.
The DOS Perspective.
Writing to Video Mode in Text Mode.
Biosequip() and _bios_equiplist()
RS-232 communications.
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VDU BASICS
Components of VDU
Monitor and video graphics adapter.
Monitor:
Refresh rate-
The microprocessor does not have the ability to send signals directly to the monitor.
Either the microprocessor or the graphics processor writes the data on the video memory.
The data on the video memory is converted to analog signals and send to CRT to get displayed.
When the electron beam strikes the phosphor coating the CRT glows.
The phosphor particle have a property that unless the electron beam again strike them they would vanish.
To over come this the graphics circuitry reads the information repeatedly and display on the screen
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VDU BASICS
The process is called refreshing the screen and the rate at which it is refreshed is called refresh rate.
Resolution:
The display resolution is defined by the number of rows from top to bottom and number of pixels from left to right on each scan.
Graphics circuitry:
The graphics adapter converts the digital information from the video memory to analog signals which gets displayed on the screen.
Category of adapters:
1. MDA (Monochrome display adapter).
2. HGC (Hercules graphics card).
3. VGA (Video graphics array).
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4. ACCEL SOFTWARE AND TECHNOLOGIES LTD.
VDU BASICS
4. CGA (Color graphics adapter).
5. EGA (Enhanced graphics adapter).
6. SVGA (Super video graphics adapter).
Modern graphics adapter:
The graphics cards are connected either to PCI or AGP.
The communication between the processor and adapter in PCI takes place through PCI bus which is shared by many devices.
AGP is not shared and is dedicated to graphics operation alone.
COMPONENTS:
Graphics processor-
The graphics processor relives the main processor from sending data to the graphics card.
The main processor sends a set of instructions to the graphics processor.
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5. ACCEL SOFTWARE AND TECHNOLOGIES LTD.
VDU BASICS
Video Memory-
The memory that holds the video image to be displayed on the screen is called video memory.
The video memory holds the information about the pixels and color of the pixels.
DAC-
The data received form the main processor is in the form of digital information which has to be converted to analog information that can be displayed on the monitor.
Graphics BIOS-
The BIOS on the rom chip coordinates the activity of the other chips available on the video card.
Color in Text Mode:
The text displayed on the screen occupies 2 byte of video memory to display each character.
The byte 1 represents the ASCII value of the text getting displayed.
The byte 2 represents the color characteristics.
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6. ACCEL SOFTWARE AND TECHNOLOGIES LTD.
VDU BASICS
The color byte contains three characteristics
1. The foreground text color.
2. The background color.
3. The blinking component.
purpose
Blue f/g color
Green f/g color
Red f/g color
Intensity of f/g
Blue b/g color
Green b/g color
Red b/g color
blinking
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The DOS Perspective
The first four bit produces 16 different foreground color.
The next 3 bit component produces 8 different background color.
The DOS Perspective:
The DOS works under the real mode of operation.
In these mode of operation the size of the register is 16 bits so the maximum size of the segment could be 64k.
In DOS 2 blocks of memory A block and B block each of 64kb are reserved to access the video memory.
Any thing that has to be displayed on the screen has to be written in these memory location.
WRITING TO VIDEO MEMORY IN TEXT MODE
There are three different methods for displaying character on the screen.
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8. WRITING TO VIDEO MEMORY IN TEXT MODE
a. using standard library routine.
b. using ROM-BIOS or DOS routine.
c. writing character directly into video memory.
The block B is used is used for displaying character in text mode.
Each character to be displayed occupies 2 bytes in memory.
E.g
If ‘A’ is displayed in the 0th row and 0th column on the screen if the address is 0xB8000 the next address contains the color attribute of the character.
About (80*25*2) which is 4000 bytes of memory is occupied for the total display on the screen.
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9. WRITING TO VIDEO MEMORY IN TEXT MODE
E.g Screen full of ‘A’:
main() {
int I;
char far *scr = 0xB L;
for(I=0;I<=3999;I=I+2);
*(scr+I)=‘A’; }
E.g changing the color of a character:
for(I=1;I<=3999;I=I+2);
*(scr+I)=112;
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10. Biosequip() and _bios_equiplist()
Biosequip() and _bios_equiplist() use BIOS interrupt 0x11 to return an integer describing the equipment connected to the system.
The return value is interpreted as a collection of bit-sized fields.
E.g
Declaration:
int biosequip(void);
unsigned _bios_equiplist(void);
Let us see how the bit fields are manipulated
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EQUIPMENT BIOS CALLS
Interrupt INT 11H is used to determine the hardware attached to the computer system. It returns a value in register AX, which is comprised as follows,
Bits Description
15, Number of printers 00=0, 01=1 &so on
Serial printer attached
Game I/O attached
11,10, Number of RS232 cards attached
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EQUIPMENT BIOS CALLS
DMA 0=m/c has DMA,1= m/c has no DMA
7, Number of disk drives 00=1, 01=2, 10=3, 11=4
5, Initial video mode 00=40, 01=80, 11=Mono
3, Ram Size 00=16k, 01=32k,10=48k, 11=64k
Co-Processor
IPL from disk 1=disk, 0=None
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Bit field format
Number of parallel printers 00 = 0; 01 = 1; 10 = 2; 11 = 3
Serial printer attached
Game I/O attached
Number of COM ports: 000 = 0, 001 = 1,..., 111 = 7
Direct memory access (DMA)
0 = Machine has DMA;
1 = Machine doesn't have DMA
Number of disk drives:
00 = 0; 01 = 1; 10 = 2; 11 = 3
Initial video mode
00 = Unused
01 = 40x25 BW with color card
10 = 80x25 BW with color card
11 = 80x25 BW with mono card
Motherboard RAM size Floating-point coprocessor
00 = 16K; 01 = 32K; 10 = 48K; 11 = 64K Boot from disk 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
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EQUIPMENT BIOS CALLS
Eg: Calls to the ROM BIOS Int 11h to check whether math coprocessor is installed.
#include <dos.h>
#include <stdio.h>
union REGS regs;
main() {
int86(0x11,&regs,&regs);
int equip_check =regs.x.ax;
if(equip_check & 0x002)
printf(“\n there is a math coprocessor installed “);
else
printf(“\n no math coprocessor installed “); }
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Memory size
Both biosmemory() and _bios_memsize() use BIOS interrupt 0x12 to return the size of RAM.
Declaration:
int biosmemory(void);
unsigned _bios_memsize(void);
E.g 1
#include <bios.h>
int main(void) {
int memory_size;
memory_size = biosmemory();
printf("RAM size = %d K",memory_size);
return 0; }
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Memory size
E.g 2
#include <bios.h>
int main(void) {
unsigned memory_size;
memory_size = _bios_memsize();
printf("RAM size = %d K\n", memory_size);
return 0; }
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RS-232 communications
Both bioscom and _bios_serialcom use BIOS interrupt 0x14 to perform various RS-232 communications over the I/O port given in port.
Arg What It Is/Does
abyte OR combination of bits that specifies COM port settings
(ignored if cmd = 2 or 3)
cmd Specifies the I/O operation to perform
port Identifies the I/O port; 0 = COM1, 1 = COM2, etc.
Declaration:
int bioscom(int cmd, char abyte, int port);
unsigned _bios_serialcom(int cmd, int port, char abyte);
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Cmd argument settings
cmd can be one of the following
Bioscom _bios_serialcom What Function Does
_COM_INIT Sets the communications parameters to the value in abyte.
1 _COM_SEND Sends the character in abyte out over the
communications line
2 _COM_RECEIVE Receives a character from the communications line.
3 _COM_STATUS Returns current status of the communications port
For all values of cmd, both functions return a 16-bit integer.
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More on cmd
When cmd = 2 or 3 (_COM_RECEIVE or _COM_STATUS), the abyte argument is ignored.
When cmd = 0 (_COM_INIT), abyte is an OR combination of the following bits (one from each group).
bioscom
_bios_serialcom
Meaning
0x02
0x03
_COM_CHR7
_COM_CHR8
7 data bits
8 data bits
0x00
0x04
_COM_STOP1
_COM_STOP2
1 stop bit.
2 stop bits.
0x08
0x18
_COM_NOPARITY
_COM_ODDPARITY
_COM_EVENPARITY
No parity
Odd parity
Even parity
0x20
0x40
_COM_110
_COM_150
_COM_300
110 baud
150 baud
300 baud
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More on cmd
example, if
abyte = 0xEB = (0xE0 | 0x08 | 0x00 | 0x03)
= (_COM_9600 | _COM_ODDPARITY | _COM_STOP1 | _COM_CHR8)
The communications port is set to
9600 baud (0xE0 = _COM_9600)
Odd parity (0x08 = _COM_ODDPARITY)
1 stop bit (0x00 = _COM_STOP1)
8 data bits (0x03 = _COM_CHR8)
0x60
0x80
0xA0
0xC0
0xE0
_COM_600
_COM_1200
_COM_2400
_COM_4800
_COM_9600
600 baud
1200 baud
2400 baud
4800 baud
9600 baud
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16 Bit status register
15. Time out (set to 1 if abyte value could not be sent)
14. Transmit shift register empty.
13. Transmit holding register empty.
12. Break detect.
11. Framing error.
10. Parity error.
09. Overrun error
08. Data ready. (status bits)
07. Change in clear to send.
06. Change in data set ready. (lower bits)
05. Trailing edge ring detector.
04. Change in receive line signal detector
03. Clear to send.
02. Data set ready.
01. Ring indicator.
00. Received line signal detect 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
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_BIOS_SERIALCOM()
#include <bios.h>
#include <conio.h>
#define COM
#define DATA_READY 0x100
#define TRUE
#define FALSE
#define SETTINGS (_COM_1200 | _COM_CHR7 | _COM_STOP1 | _COM_NOPARITY)
int main(void) {
unsigned in, out, status;
_bios_serialcom(_COM_INIT, COM1, SETTINGS);
printf("... _BIOS_SERIALCOM [ESC] to exit ...\r\n");
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23. ACCEL SOFTWARE AND TECHNOLOGIES LTD.
_BIOS_SERIALCOM()
for (;;) {
status = _bios_serialcom(_COM_STATUS, COM1, 0);
if (status & DATA_READY)
if ((out = _bios_serialcom(_COM_RECEIVE, COM1, 0) & x7F) != 0)
putch(out);
if (kbhit())
if ((in = getch()) == '\x1B')
break;
_bios_serialcom(_COM_SEND, COM1, in); }
return 0;
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