EPROM increases spead of state machines

HL1.OCT–RM–Cypress Semiconductor

EPROM increases speed of state machines

Internal feedback shortens loop, allows 83-MHz operation

The CY7C258/9 EPROMs combine registered inputs and outputs with an
internal feedback path and a 2-K x 16-bit memory array. The internal
feedback path removes off-chip delays from the loop when the devices are
used to make state machines. Both input and output registers can be
bypassed, bit by bit. Eleven of the 16 data-out lines feed back, where
they may substitute for any of the 11 address lines. The 258 version has
output pins for D_{0 through D} 7, with D_8-D 15 only
available for feedback. The 259, on the other hand, has pins for all 16
outputs (see diagram). The address multiplexer can connect each address
bit to either a feedback line or an input pin. Therefore multiple
independent simple state machines can be created in one chip. The
bypassable input registers mean input changes can pass through the array
immediately or be synchronized. Output bits that are not used for
feedback can bypass the register if desired, making a Mealy machine. If
output as well as feedback bits are registered, the result is called a
Moore machine. The user can mix Mealy and Moore outputs on the same state
machine. The input registers have programmable timing specs. Depending on
the requirements of the source device, an input can have 3-ns setup and
hold times, or a 7-ns setup with 0 hold. The minimum cycle time of the
fastest commercial grade is 12 ns. Because it is a memory, the EPROM has
bits available to indicate every possible 11-input state. No minimization
is required. Any means of generating the desired states can be used, such
as high-level computer languages. However, common PLD design tools can
also be used. (CY7C258, 28-pin PLCC, $29.05 ea/100; CY7C259, 44-pin PLCC,
$40.60 ea/100–available now.) Cypress Semiconductor Corp. San Jose, CA
John Whitinger 408-943-2817

CAPTION:

Registered EPROMs with internal feedback, the CY7C258/9 can implement
state machines twice as fast as similar parts with feedback off the chip.