CM1K Hardware User’s Manual
39
6.1
Clocks, power-up and reset
6.1.1
G_Reset, global reset
The CM1K 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, the recognition stage and the i2c slave controller so all registers are set to
their default values. In a multi-chip configuration, the same G_RESET_ must be connected to all chips.
6.1.2
G_CLK, system clock
The CM1K operates at a typical system clock of 27 MHz. If multiple CM1K are connected in parallel the typical
system clock is 16 Mhz.
6.1.3
CS_, power saving control line
The CS_ line controls the propagation of the system clock G_CLK to the neurons, the reco_logic and the i2c slave
controller of the chip. It is pulled low by default letting the clock run continuously.
Pulling up the the CS_ line when the CM1K is unused reduces considerably its power consumption (from 500 mW
to 25 mW). On the other hand the timings to pull CS_ back down and let the system clock pass through must be
accurate: (1) It must be pulled down on a negative edge of G_CLK when the external data strobe (DS) is pulled up
at the latest. (2) It must be released on the negative edge of the system clock following the rise of the RDY signal at
the earliest or the fall of the B_BSY signal.
6.2
Neural network BiDir lines (parallel bus)
The parallel bus is used to transmit the Read/WriteRegister commands to all the neurons at once. It is composed of
26 lines:
DS
Data strobe signal
1
RW_
Read/Write signal
1
REG
5-bit register value
5
DATA
16-bit data value
16
RDY
Ready control signal
1
ID_
Identified control signal (see Erratum)
1
UNC_
Uncertain control signal necessary to learn
1
The neurons sample these signals on the positive edge of the system clock G_CLK. Their setup time must be at
least 5 nanoseconds before the positive edge of G-Clock. The hold time must be at least 5 nanoseconds after the
positive edge of the clock. The signals have to be released before the next positive edge of the clock to ensure that
the data bus becomes bi-directional for proper execution of the commands requiring snooping of the bus.
Up to eight CM1K running at a system clock of 16Mhz can be connected to the same parallel bus without any re-
drive. Beyond a chain of 8 CM1K chips, buffers must be inserted.