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Atmel AVR910, Application Note

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Atmel AVR910 Application Note Download Page 10

10

0943E–AVR–08/08

AVR910

A Simple Low-cost 
In-System 
Programmer

This application note will not discuss all aspects of an In-System Programmer. Instead, it will
show how a simple low-cost programmer can be made, using only an AT90S1200 and a few dis-
crete components.

The programmer will plug into any serial port of any PC. The AT90S1200 doesn’t come with a
hardware UART, but the software will run a half duplex UART by using the Timer/Counter0 to
clock data. The AT90S1200 also takes care of programming the target AVR by running the Mas-
ter SPI entirely in software.

The schematics to the programmer can be seen in Figure 4. Power to the AT90S1200 is taken
from the target system. The negative voltage needed to communicate serially with the PC is
stored in C100 when receiving a logical one (negative line voltage).

The transmit line is fed with this negative voltage from C100, when transistor Q100 is closed.
This sends a logical one on the transmit line. Logical zeros (positive voltage) is sent by opening
Q100, connecting V

CC

 (actually V

CC

 - 0.2V) to the transmit line.

Some older PC systems might have serial port not accepting voltages below +10 volts as logical
zero. This, however, is not a problem with the majority of existing PCs.

The file avr910.asm contains the firmware for the AT90S1200.

Figure 4.  A Low-cost In-System Programmer

U100

AT90

S

1200

GND

AIN0/PB0

AIN1/PB1

PB2

PB

3

PB4

PB5

PB6

PB7

XTAL2

VCC

RE

S

ET

PD0

PD1

PD2/INT0

PD

3

PD4

PD5

PD6

XTAL1

10

12

1

3

14

15

16

17

1

8

19

4

20

1

2

3

6

7

8

9

11

5

1M0

R106

XC100

4 MH

Z

VCC

MO

S

I

GND

J101

2

4

6

1

3

5

MI

S

O

S

CK

RE

S

ET

CONNECTOR A

S

S

EEN FROM BELOW

GND

C101

100N

R10

3

4K7

R102

4K7

4K7

4K7

PAD

R

X

D

T

X

D

R101

4K7

R100

4K7

BC

8

47C

Q101

R105

D101

BA

S

16

BA

S

16

D100

20V

1.0

u

F

+

C100

RECEIVE

TRAN

S

MIT

1

2

3

6

7

5

4

8

9

9-PIN D-

S

UB

FEMALE

R104

J100

BC

8

57C

Q100

Summary of Contents for AVR910

Page 1: ...target AVR microcontroller to be programmed from any PC equipped with a regular 9 pin serial port Alternatively the entire In System Programmer can be built into the system allowing it to reprogram itself The Programming Interface For In System Programming the programmer is connected to the target using as few wires as possible To program any AVR microcontroller in any target system a simple Six w...

Page 2: ...Connector Layout Top View Hardware Design Considerations To allow In System Programming of the AVR microcontroller the In System Programmer must be able to override the pin functionality during programming This section describes the details of each pin used for the programming operation GND The In System Programmer and target system need to operate with the same reference voltage This is done by c...

Page 3: ...did not echo back give Reset a positive pulse and issue a new Programming Enable command Note that all four bytes of the of the Programming Enable command must be sent before starting a new transmission The target AVR microcontroller will always set up its SCK pin to be an input with no pull up whenever Reset is active See also the description of the Reset wire Table 1 Connections Required for In ...

Page 4: ...e its power supplied from the programmer through the same connector used for the communication This would allow the target to be programmed without applying power to the target externally Programming Protocol Immediately after Reset goes active on the target AVR microcontroller the chip is ready to enter Programming mode The internal Serial Peripheral Interface SPI is activated and is ready to acc...

Page 5: ... the protecting Lock bits The target AVR microcontroller will not respond with an acknowledge to the Programming Enable command To check if the command has been accepted by the target AVR microcon troller the device code could be read The device code is also known as the signature bytes Device Code After the Programming Enable command has been successfully read by the SPI interface the programmer ...

Page 6: ...or high byte with the H bit in the command byte 0 is low 1 is high byte The byte stored at this address is then returned from the target AVR microcontroller in byte 4 Usually each 16 bit word in Flash contains one AVR instruction Assuming the instruction stored at address 104 is add r16 r17 the op code for this instruction would be stored as 0F01 Reading address 104 serially the expected result re...

Page 7: ...e devices there is no method to detect when the Flash write cycle has ended For this reason the programmer presented in this application note waits N ms before attempting to send another command to the interface the delay N will depend on target device and can be found in the programming section of the datasheet For some devices it is possible to use polling When a byte is being programmed into th...

Page 8: ...tected from further writing or you may completely disable both reading and writing of memories on the chip In some devices the Lock bits can not be read and setting Lock bits can not be verified by the programmer To check that the Lock bits have been set properly in these devices one should attempt to alter a location in EEPROM When Lock bit 1 is set memory locations are not altered When both Lock...

Page 9: ... setting a bit to one Erasing the memory is performed with the Chip Erase command This command will erase all memory contents both Flash Program Memory and EEPROM Only after a successful erase of the memory the Lock bits will be erased This method ensures that data in the memories are kept secured until all data have been completely erased After a Chip Erase all memory contents will be read as FF ...

Page 10: ...tive line voltage The transmit line is fed with this negative voltage from C100 when transistor Q100 is closed This sends a logical one on the transmit line Logical zeros positive voltage is sent by opening Q100 connecting VCC actually VCC 0 2V to the transmit line Some older PC systems might have serial port not accepting voltages below 10 volts as logical zero This however is not a problem with ...

Page 11: ... 6 PIN HEADER IDC FEMALE CABLE MOUNT 1 Q100 45V 100MA BC857C PHILIPS SMD NPN TRANSISTOR SO 23 PACKAGE 1 Q101 45V 100MA BC847C PHILIPS SMD PNP TRANSISTOR SO 23 PACKAGE 6 R100 105 4K7 R08_4K7 1 KOA RESISTOR 0 125W 1 0805 1 R106 1M0 NOT_USED 1 KOA RESISTOR 0 125W 1 0805 1 U100 SOIC 20 AT90S1200 4SC ATMEL AVR MICROCONTROLLER 20 PIN SOIC 1 XC100 4 0MHZ CSTCC4 00MG 0 5 MURATA AVX CERAMIC RESONATOR 4 00 ...

Page 12: ...OR STATUTORY WARRANTY RELATING TO ITS PRODUCTS INCLUDING BUT NOT LIMITED TO THE IMPLIED WARRANTY OF MERCHANTABILITY FITNESS FOR A PARTICULAR PURPOSE OR NON INFRINGEMENT IN NO EVENT SHALL ATMEL BE LIABLE FOR ANY DIRECT INDIRECT CONSEQUENTIAL PUNITIVE SPECIAL OR INCIDEN TAL DAMAGES INCLUDING WITHOUT LIMITATION DAMAGES FOR LOSS OF PROFITS BUSINESS INTERRUPTION OR LOSS OF INFORMATION ARISING OUT OF TH...

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