Lattice Semiconductor MachXO2 Series Usage Manual page 6

SEDDONE
SEDDONE is an output which indicates that SED checking has completed a cycle. This signal is an active high out-
put from the SED hardware, clocked out on the rising edge of SEDCLKOUT. SEDDONE will be reset by a low SED-
START signal.
SEDINPROG
SEDINPROG is an output which indicates that SED checking is in progress. This signal is an active high output
from the SED hardware, clocked out on the rising edge of SEDCLKOUT. SEDINPROG will go high following SED-
START going high after the delay shown in Figure 5.
SEDERR
SEDERR is an output which indicates that SED checking has completed a cycle with an error. This signal is an
active high output from the SED hardware, clocked out on the rising edge of SEDCLKOUT. SEDERR will be reset
by a low SEDSTART signal and delay as defined in Figure 5.
SED Flow
The general SED flow once VCC reaches the data sheet Vcc minimum recommend level is as follows.
1. User logic sets SEDENABLE high. This signal may be tied high if desired.
2. User logic sets SEDSTART high and holds it high for the duration of the SED cycle. SEDINPROG goes
high. If SEDDONE or SEDERR are already high they will be driven low.
3. SED starts reading back data from the configuration SRAM.
4. SED finishes checking. SEDERR is updated, SEDINPROG goes low, SEDDONE goes high and another
SED cycle is started by asserting SEDSTART. When SEDSTART is asserted the SEDERR signal will be
reset.
5. If SEDERR is driven high it can be reset by reconfiguring the PLD.
6. SEDENABLE goes low when/if the user specifies, and SED is no longer in use.
The preferred action to take when an error is detected is to reconfigure the PLD. Reconfiguration can be accom-
plished by driving the PROGRAMN pin low. This can be done by externally connecting a GPIO pin to PROGRAMN.
Figure 4. Example Schematic
MachXO2
PROGRAMN
Note: The 1 Ohm resistor shown allows a user to recover from a bad program
which always pulls the GPIO pin low in the MachXO2 device. If this type of pattern
is loaded into the MachXO2, the device will always be held in the re-configuration
state and is not able to communicate or be erased to clear the error condition.
To recover from this condition, remove the resistor and reprogram the device,
then replace resistor.
VCC
10K
1 Ohm
GPIO
Open Drain
Output
6
MachXO2 SED Usage Guide