Datasheet

359
ATmega16U4/32U4 [DATASHEET]
Atmel-7766J-USB-ATmega16U4/32U4-Datasheet_04/2016
28.6 Parallel Programming
28.6.1 Enter Programming Mode
The following algorithm puts the device in parallel programming mode:
1. Apply 4.5 - 5.5V between V
CC
and GND.
2. Set RESET
to “0” and toggle XTAL1 at least six times.
3. Set the Prog_enable pins listed in
Table 28-8 on page 358 to “0000” and wait at least 100ns.
4. Apply 11.5 - 12.5V to RESET
. Any activity on Prog_enable pins within 100ns after +12V has been applied
to RESET
, will cause the device to fail entering programming mode.
5. Wait at least 50µs before sending a new command.
28.6.2 Considerations for Efficient Programming
The loaded command and address are retained in the device during programming. For efficient programming,
the following should be considered.
 The command needs only be loaded once when writing or reading multiple memory locations
 Skip writing the data value 0xFF, that is the contents of the entire EEPROM (unless the EESAVE Fuse is
programmed) and Flash after a Chip Erase
 Address high byte needs only be loaded before programming or reading a new 256 word window in Flash
or 256 byte EEPROM. This consideration also applies to Signature bytes reading.
28.6.3 Chip Erase
The Chip Erase will erase the Flash and EEPROM
(1)
memories plus Lock bits. The Lock bits are not reset until
the program memory has been completely erased. The Fuse bits are not changed. A Chip Erase must be
performed before the Flash and/or EEPROM are reprogrammed.
Note: 1. The EEPRPOM memory is preserved during Chip Erase if the EESAVE Fuse is programmed.
Load Command “Chip Erase”:
1. Set XA1, XA0 to “10”. This enables command loading.
2. Set BS1 to “0”.
3. Set DATA to “1000 0000”. This is the command for Chip Erase.
4. Give XTAL1 a positive pulse. This loads the command.
Table 28-11. No. of Words in a Page and No. of Pages in the Flash
Device Flash Size Page Size PCWORD
No. of
Pages
PCPAGE PCMSB
ATmega16U4 8K words (16KB) 64 words PC[5:0] 128 PC[12:6] 12
ATmega32U4 16K words (32KB) 64 words PC[5:0] 256 PC[13:6] 13
Table 28-12. No. of Words in a Page and No. of Pages in the EEPROM
Device EEPROM Size Page Size PCWORD
No. of
Pages
PCPAGE EEAMSB
ATmega16U4 512 bytes 4 bytes EEA[1:0] 128 EEA[8:2] 8
ATmega32U4 1KB 4 bytes EEA[1:0] 256 EEA[9:2] 9