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283
8210C–AVR–09/11
Atmel AVR XMEGA D
Next, continue to keep the PDI_DATA line high for 16 PDI_CLK cycles. The first PDI_CLK cycle
must start no later than 100µs after the RESET functionality of the Reset pin is disabled. If this
does not occur in time, the enabling procedure must start over again. The enable sequence is
shown in
.
Figure 23-3.
PDI physical layer enable sequence.
The Reset pin is sampled when the PDI interface is enabled. The reset register is then set
according to the state of the Reset pin, preventing the device from running code after the reset
functionality of this pin is disabled.
23.3.2
Disabling
If the clock frequency on PDI_CLK is lower than approximately 10kHz, this is regarded as inac-
tivity on the clock line. This will automatically disable the PDI. If not disabled by a fuse, the reset
function of the Reset (PDI_CLK) pin is enabled again. This also means that the minimum pro-
gramming frequency is approximately 10kHz.
23.3.3
Frame Format and Characters
The PDI physical layer uses a frame format defined as one character of eight data bits, with a
start bit, a parity bit, and two stop bits.
Figure 23-4.
PDI serial frame format.
Three different characters are used, DATA, BREAK, and IDLE. The BREAK character is equal
to a 12-bit length of low level. The IDLE character is equal to a 12- bit length of high level. The
BREAK and IDLE characters can be extended beyond the 12-bit length.
Disable RESET function on Reset (PDI_CLK) pin
Activate PDI
PDI_DATA
PDI_CLK
St
Start bit, always low
(0-7)
Data bits (0 to 7)
P
Parity bit, even parity used
Sp1
Stop bit 1, always high
Sp2
Stop bit 2, always high
St
0
1
2
3
4
5
6
7
P
Sp1
FRAME
Sp2
(IDLE)
(St/IDLE)