NM500 Manual
14
3.1
CLOCKS, POWER-UP AND RESET
3.1.1
G_RESET, GLOBAL RESET
The chip is reset at power-up by pulling down the G_RESET_l pin for a minimum of 5 clock cycles. An internal reset
signal is then sustained for 255 clock cycles to filter any bouncing of the G_RESET_l external pulse. It is propagated
internally to the neurons so all registers are set to their default values. In a multi-chip configuration, the same
G_RESET_ must be connected to all chips.
3.1.2
G_CLK, SYSTEM CLOCK
The chip operates at a typical system clock of 35 MHz. If multiple chips are connected in parallel the typical system
clock is 18 Mhz.
3.1.3
CS_, POWER SAVING CONTROL LINE
The CS_ line controls the propagation of the system clock G_CLK to the neurons. It is pulled low by default letting
the clock run continuously.
Pulling up the the CS_ line when the chip is unused reduces considerably its power consumption (from 500 mW to
25 mW).
The timings to pull CS_ down and let the system clock pass through must be accurate:
-
It must be pulled down on a negative edge of the clock when the external data strobe (DS) is high.
-
It must be released on the negative edge of the clock following the rise of the RDY signal at the earliest.
3.1.4
DCI
Until the DCI line of a chip is high, its neurons are idle. As soon as the DCI line rises, the neurons of the chip
become active, meaning ready to learn and recognize.
In a configuration with multiple chips, the Daisy-Chain-In (DCI) line of the first chip must be high. For the
subsequent chips, the connection between their DCO and DCI lines allows to physically arrange them in a chain.
The DCI line of a chip must be connected to the DCO of the previous chip in the chain. Its status is then controlled
by the neurons of the previous chip.
3.1.5
DCO
The Daisy-Chain-Out (DCO) line of a chip must be connected to the DCI of the next chip in the chain, if applicable. It
is low by default and will rise when the last neuron of the chip gets committed. If this line is connected to the DCI
of another chip, the later will awake its neurons to become Ready-To-Learn.
