Serial Downloading
Both the Flash and EEPROM memory arrays can be programmed using the serial SPI bus while RESET is pulled to GND. The serial interface consists of pins SCK, MOSI (input) and MISO (output). After RESET is set low, the Programming Enable instruction needs to be executed first before program/erase operations can be executed. NOTE, in Table 58 on page 120, the pin mapping for SPI programming is listed. Not all parts use the SPI pins dedicated for the internal SPI interface. Note that throughout the description about Serial downloading, MOSI and MISO are used to describe the serial data in and serial data out respectively.
Serial Programming Pin
Mapping
Table 58. Pin Mapping Serial Programming
Symbol |
Pins |
I/O |
Description |
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MOSI |
PB0 |
I |
Serial data in |
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MISO |
PB1 |
O |
Serial data out |
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SCK |
PB2 |
I |
Serial clock |
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Figure 67. Serial Programming and Verify(1)
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2.7 - 5.5V |
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VCC |
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2.7 - 5.5V(2) |
MOSI |
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PB0 |
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MISO |
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AVCC |
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PB1 |
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SCK |
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PB2 |
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XTAL1 |
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GND |
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Notes: 1. If the device is clocked by the internal oscillator, there is no need to connect a clock source to the XTAL1 pin.
2. VCC -0.3V < AVCC < VCC +0.3V, however, AVCC should always be within 2.7 - 5.5V.
When programming the EEPROM, an auto-erase cycle is built into the self-timed programming operation (in the serial mode ONLY) and there is no need to first execute the Chip Erase instruction. The Chip Erase operation turns the content of every memory location in both the Program and EEPROM arrays into $FF.
Depending on CKSEL Fuses, a valid clock must be present. The minimum low and high periods for the serial clock (SCK) input are defined as follows:
Low: > 2 CPU clock cycles for fck < 12 MHz, 3 CPU clock cycles for fck ≥ 12 MHz High: > 2 CPU clock cycles for fck < 12 MHz, 3 CPU clock cycles for fck ≥ 12 MHz
120 ATtiny26(L)
1477B–AVR–04/02
Serial Programming
Algorithm
ATtiny26(L)
When writing serial data to the ATtiny26, data is clocked on the rising edge of SCK.
When reading data from the ATtiny26, data is clocked on the falling edge of SCK. See Figure 68, Figure 69, and Table 69 for timing details.
To program and verify the ATtiny26 in the serial programming mode, the following sequence is recommended (See four byte instruction formats in Table 60):
1.Power-up sequence:
Apply power between VCC and GND while RESET and SCK are set to “0”. In some systems, the programmer can not guarantee that SCK is held low during Power-up. In this case, RESET must be given a positive pulse of at least two CPU clock cycles duration after SCK has been set to “0”.
2.Wait for at least 20 ms and enable serial programming by sending the Programming Enable serial instruction to pin MOSI.
3.The serial programming instructions will not work if the communication is out of synchronization. When in synchronize the second byte ($53), will echo back when issuing the third byte of the Programming Enable instruction. Whether the echo is correct or not, all 4 bytes of the instruction must be transmitted. If the $53 did not echo back, give RESET a positive pulse and issue a new Programming Enable command.
4.The Flash is programmed one page at a time. The memory page is loaded one byte at a time by supplying the 4 LSB of the address and data together with the Load Program Memory Page instruction. To ensure correct loading of the page, the data low byte must be loaded before data high byte is applied for given address. The Program Memory Page is stored by loading the Write Program Memory Page instruction with the 6 MSB of the address. If polling is not used,
the user must wait at least tWD_FLASH before issuing the next page. (See Table 59). Accessing the serial programming interface before the Flash write operation completes can result in incorrect programming.
5.The EEPROM array is programmed one byte at a time by supplying the address and data together with the appropriate Write instruction. An EEPROM memory location is first automatically erased before new data is written. If polling is not
used, the user must wait at least tWD_EEPROM before issuing the next byte. (See Table 59). In a chip erased device, no $FFs in the data file(s) need to be programmed.
6.Any memory location can be verified by using the Read instruction which returns the content at the selected address at serial output MISO.
7.At the end of the programming session, RESET can be set high to commence normal operation.
8.Power-off sequence (if needed): Set RESET to “1”.
Turn VCC power off.
121
1477B–AVR–04/02
Data Polling Flash |
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When a page is being programmed into the Flash, reading an address location within |
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the page being programmed will give the value $FF. At the time the device is ready for a |
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new page, the programmed value will read correctly. This is used to determine when the |
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next page can be written. Note that the entire page is written simultaneously and any |
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address within the page can be used for polling. Data polling of the Flash will not work |
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for the value $FF, so when programming this value, the user will have to wait for at least |
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tWD_FLASH before programming the next page. As a chip-erased device contains $FF in |
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all locations, programming of addresses that are meant to contain $FF, can be skipped. |
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See Table 59 for tWD_FLASH value. |
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Data Polling EEPROM |
When a new byte has been written and is being programmed into EEPROM, reading the |
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address location being programmed will give the value $FF. At the time the device is |
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ready for a new byte, the programmed value will read correctly. This is used to deter- |
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mine when the next byte can be written. This will not work for the value $FF, but the user |
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should have the following in mind: As a chip-erased device contains $FF in all locations, |
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programming of addresses that are meant to contain $FF, can be skipped. This does |
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not apply if the EEPROM is re-programmed without chip-erasing the device. In this |
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case, data polling cannot be used for the value $FF, and the user will have to wait at |
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least tWD_EEPROM before programming the next byte. See Table 59 for tWD_EEPROM value. |
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Table 59. Minimum Wait Delay before Writing the Next Flash or EEPROM Location |
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Symbol |
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Minimum Wait Delay |
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tWD_FLASH |
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4.5 ms |
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tWD_EEPROM |
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9.0 ms |
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tWD_ERASE |
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9.0 ms |
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Figure 68. Serial Programming Waveforms |
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SERIAL DATA INPUT |
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MSB |
LSB |
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(MOSI) |
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SERIAL DATA OUTPUT |
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MSB |
LSB |
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(MISO) |
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SERIAL CLOCK INPUT (SCK)
SAMPLE
122 ATtiny26(L)
1477B–AVR–04/02
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ATtiny26(L) |
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Table 60. Serial Programming Instruction Set |
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Instruction |
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Instruction Format |
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Operation |
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Byte 1 |
Byte 2 |
Byte 3 |
Byte4 |
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Programming Enable |
1010 1100 |
0101 0011 |
xxxx xxxx |
xxxx xxxx |
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Enable Serial Programming after |
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RESET |
goes low. |
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Chip Erase |
1010 1100 |
100x xxxx |
xxxx xxxx |
xxxx xxxx |
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Chip Erase EEPROM and Flash. |
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Read Program Memory |
0010 H000 |
xxxx xxaa |
bbbb bbbb |
oooo oooo |
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Read H (high or low) data o from |
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Program memory at word address a:b. |
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Load Program Memory Page |
0100 H000 |
xxxx xxxx |
xxxx bbbb |
iiii iiii |
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Write H (high or low) data i to Program |
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Memory page at word address b. Data |
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low byte must be loaded before data |
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high byte is applied within the same |
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address. |
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Write Program Memory Page |
0100 1100 |
xxxx xxaa |
bbbb xxxx |
xxxx xxxx |
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Write Program Memory Page at |
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address a:b. |
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Read EEPROM Memory |
1010 0000 |
xxxx xxxx |
xbbb bbbb |
oooo oooo |
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Read data o from EEPROM memory at |
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address b. |
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Write EEPROM Memory |
1100 0000 |
xxxx xxxx |
xbbb bbbb |
iiii iiii |
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Write data i to EEPROM memory at |
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address b. |
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Read Lock Bits |
0101 1000 |
0000 0000 |
xxxx xxxx |
xxxx xxoo |
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Read Lock bits. “0” = programmed, “1” |
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= unprogrammed. See Table 47 on |
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page 106 for details. |
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Write Lock Bits |
1010 1100 |
111x xxxx |
xxxx xxxx |
1111 11ii |
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Write Lock bits. Set bits = “0” to |
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program Lock bits. See Table 47 on |
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page 106 for details. |
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Read Signature Byte |
0011 0000 |
xxxx xxxx |
xxxx xxbb |
oooo oooo |
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Read Signature Byte o at address b. |
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Write Fuse Bits |
1010 1100 |
1010 0000 |
xxxx xxxx |
iiii iiii |
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unprogram. See Table 50 on page |
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107 for details. |
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Write Fuse High Bits |
1010 1100 |
1010 1000 |
xxxx xxxx |
xxxi iiii |
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Set bits = “0” to program, “1” to |
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unprogram. See Table 49 on page |
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107 for details. |
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Read Fuse Bits |
0101 0000 |
0000 0000 |
xxxx xxxx |
oooo oooo |
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Read Fuse bits. “0” = programmed, “1” |
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= unprogrammed. See Table 50 on |
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page 107 for details. |
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Read Fuse High Bits |
0101 1000 |
0000 1000 |
xxxx xxxx |
xxxo oooo |
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Read Fuse high bits. |
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“0” = programmed, |
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“1” = unprogrammed. See Table 49 |
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on page 107 for details. |
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Read Calibration Byte |
0011 1000 |
xxxx xxxx |
0000 00bb |
oooo oooo |
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Read Calibration Byte o. |
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Note: a = address high bits |
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b = address low bits |
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H = 0 – Low byte, 1 – High Byte o = data out
i = data in
x = don’t care
123
1477B–AVR–04/02
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Serial Programming |
Figure 69. Serial Programming Timing |
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Characteristics |
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MOSI
t |
OVSH |
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t |
tSLSH |
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SHOX |
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SCK
t SHSL
MISO
t SLIV
Table 61. Serial Programming Characteristics, TA = -40°C to 85°C, VCC = 2.7V - 5.5V (Unless Otherwise Noted)(1)
Symbol |
Parameter |
Min |
Typ |
Max |
Units |
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1/tCLCL |
Oscillator Frequency (VCC = 2.7 - 5.5 V) |
0 |
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MHz |
tCLCL |
Oscillator Period (VCC = 2.7 - 5.5 V) |
125 |
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1/tCLCL |
Oscillator Frequency (VCC = 4.5 - 5.5 V) |
0 |
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MHz |
tCLCL |
Oscillator Period (VCC = 4.5 - 5.5 V) |
62.5 |
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tSHSL |
SCK Pulse Width High |
(1) |
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2 tCLCL |
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tSLSH |
SCK Pulse Width Low |
(1) |
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2 tCLCL |
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tOVSH |
MOSI Setup to SCK High |
tCLCL |
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tSHOX |
MOSI Hold after SCK High |
2 tCLCL |
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tSLIV |
SCK Low to MISO Valid |
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Note: 1. |
2 tCLCL for fck < 12 MHz, 3 tCLCL for fck >= 12 MHz |
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124 ATtiny26(L)
1477B–AVR–04/02