fplds

Three FPLD Types• Simple Programmable Logic Device (SPLD)

– LSI device

– Less than 1000 logic gates

• Complex Programmable Logic Device (CPLD)– VLSI device

– Higher logic capacity than SPLDs

• Field Programmable Gate Array (FPGA)– VLSI device

– Higher logic capacity than CPLDs

1

ProgrammableLogic Devices

(FPLDs)

CPLDsSPLDs(e.g., PALs) FPGAs

Three FPLD Types• Simple Programmable Logic Device (SPLD)

– PLA or PAL

– Fixed internal routing, deterministic propagation delays

• Complex Programmable Logic Device (CPLD)– Multiple SPLDs onto a single chip

– Programmable interconnect

• Field Programmable Gate Array (FPGA)– An array of logic blocks

– Large number of gates, user selectable interconnection, delays depending on design and routing

– A high ratio of flip-flops to logic resources

2


(FPLDs)


SPLDs

• SPLDs = Simple PLDs• Popular SPLD Architecture Types

– Programmable Logic Array, PLA– Programmable Array Logic, PAL (Vantis)– General Array Logic, GAL (Lattice)– others

• Architecture Differences– AND versus OR implementation– Programmability (e.g., EE)– Fundamental logic block

3


(FPLDs)


SPLDs• We have already taken a close

look at SPLDs• A PLA-like SPLD is illustrated

at left– PAL and GAL devices offered

a somewhat better solution

• SPLDs are good alternative to using SSI and MSI devices– Especially if re-programmable

4

Logic Functions

Product Terms

Sums


(FPLDs)


SPLDs• Conventional programmable logic

– PALs, PLAs, GALs– standard parts like GAL22V10 and PAL16R4 are available from

multiple vendors

• Includes programmable logic cells to a limited degree (programming options in I/O cells, may have fixed AND/OR gates for logic), limited routing network

• Lowest density of all programmable devices, however, can offer very high performance

5


(FPLDs)


• SPLDs have nearly replaced TTL logic which was the dominate approach to logic implementation

6

How to Expand SPLD Architecture?• Increase number of inputs and outputs in a

conventional PLD?– e.g., 16V8 → 20V8 → 22V10

– Why not → 32V16 → 128V64 ?

• Problems: – n times the number of inputs and outputs requires n2 as

much chip area – too costly

– logic gets slower as number of inputs to AND array increases


(FPLDs)


7

How to Expand SPLD Architecture?• Solution:

– Multiple SPLDs with a relatively small programmable interconnect

– Less general than a single large PLD

– Can use software “fitter” to partition into smaller PLD blocks


(FPLDs)


CPLD Architecture

CPLDs• PALs and GALs are available only in small sizes

– equivalent to a few hundred logic gates

• For bigger logic circuits, complex PLDs or CPLDs can be used.

• CPLDs contain the equivalent of several PALs/GALs – linked by programmable interconnections– all in one integrated circuit (IC)

• CPLDs can replace thousands, or even hundreds of thousands, of individual logic gates – increased integration density

8


(FPLDs)


Complex PLDs• Some CPLDs are programmed using a PAL

programmer, but this method becomes inconvenient for devices with hundreds of pins.

• A second method of programming is to solder the device to its printed circuit board, then feed it with a serial data stream from a personal computer.

• The CPLD contains a circuit that decodes the data stream and configures the CPLD to perform its specified logic function.

9


(FPLDs)


• Xilinx, for example:• Xilinx CPLD devices that are cheaper and have fewer

gates than Xilinx FPGAs• Meant for interfacing rather than heavy computation• Built-in flash memory

– Compare to FPGA which needs external configuration memory

• Xess board has XC9572XL part– Approximately $2-$7 in quantities of one – vs. ~$15-20 for the Spartan2 FPGA on the board– Larger quantities much lower– 1600 gates, 72 registers

Complex PLDs versus FPGAs

10


(FPLDs)


11

CPLD Architecture• Simplified CPLD

architecture• Small number of largish

PLDs (e.g., “36V18”) on a single chip

• Programmable interconnect between PLDs

• Large number of I/O blocks

• Large number of pins

CPLDs• Composition of Complex PLDs

– typically composed of 2-64 SPLDs

– interconnected using sophisticated logic

– includes macrocells (more about these later)

– includes input/output blocks

• Economical for designing large systems• Fast – switching speed

12


(FPLDs)


CPLDs

• Complex PLD's have arrays of PLD's on one chip, with an interconnection matrix connecting them.

• Timing performance can be more predictable than FPGAs because of simpler interconnect structure.

• Density is normally less than most FPGAs (although high end CPLDs will have about the same density as low-end FPGAs).


(FPLDs)


• Performance of CPLDs is usually better than FPGAs, but depends on vendor, number of cells in CPLD, and compared FPGA.

13

14

CPLD Families• Identical individual PLD blocks (Xilinx “FBs”) replicated

in different family members– Different number of PLD blocks

– Different number of I/O pins

Xilinx Xilinx XC9500 XC9500 CPLD CPLD SeriesSeries

Typical CPLD Packages• CPLDs are made using 2 to 64 SPLDs • Packages use 44-pins to over 200-pins (or more)

15

Typical CPLD Packages• QFP = Quad Flat Package – A QFP is an IC package with leads extending from each of

the four sides.

– It is used primarily for surface mounting, no socketing

• TQFP = Thin Quad Flat Package • PQFP = Plastic Quad Flat Package • VQFP = Very small Quad Flat Package

• PLCC = Plastic Leaded Chip Carrier – A package related to QFP

– Similar but has pins with larger distance, curved up underneath a thicker body to simplify socketing

16

CPLD Package Types• CSP = Chip Scale Package

– IC package with an area no greater than 1.2 times that of the die

• BGA = Ball Grid Array – A type of surface-mount packaging used for ICs

– Pins are replaced by balls of solder stuck to the bottom of the package

– The device is placed on a PCB that carries copper pads in a pattern that matches the solder balls

– The assembly is then heated causing the solder balls to melt

17

18

CPLD Families• Many CPLDs have fewer

I/O pins than macrocells– “Buried” Macrocells – provide

needed logic terms internally but these outputs are not connected externally

– IC package size dictates number of I/O pins but not the total number of macrocells

– Typical CPLD families have devices with differing resources in the same IC package

Xilinx CPLDs• Notice overlap in resource availability in a particular

package.

19

XC9572 CPLD Part Numbers• The part number for Xilinx CPLD devices includes

information as follows:

20

XC9500 CPLD Block Diagram• The XC9500 CPLD

family provides advanced in-system programming and test capabilities for high performance, general purpose logic integration.

• All devices are in-system programmable for a minimum of 10,000 program/erase cycles.

21

9500-Family Function Blocks (FBs)• 18 macrocells per FB• 36 inputs per FB (partitioning challenge, but also

reason for relatively compact size of FBs)• Macrocell outputs can go to I/O cells or back into

switch matrix to be routed to this or other FBs

22

9500-Series Macrocell• 18 macrocells per Function Block

23

Up to 5 product termsUp to 5 product terms

Programmable inversion Programmable inversion or XOR product termor XOR product term

Global clock or product-term clockGlobal clock or product-term clock

Set controlSet control

Reset controlReset control

OE controlOE control

9500-Series Product-Term Allocator• Share terms from above and below

24

programmableprogrammablesteeringsteeringelementselements

XC9500 Family

25

• An I/O block is composed of input buffer, output buffer, multiplexer for the output control and grounding control

• Slew rate control is used to smooth the rising and the falling edges of the output pulse.

• Grounding control is used to make the input/output pin (I/O) an earth ground (noise suppression).

• Each input/output pin can handle a 24-mA current.

9500-Series I/O Block• OE Multiplexer (OE

MUX) controls an output enable or stop.

• It is controlled by the signal from the macrocell or the signal from the GTS (Global Three-State control) pin.

• There are four GTS in XC95216 and XC95288 two in the others.

26

Switch Matrix for XC95108• Could be anything from a limited set of multiplexers to

a full crossbar– Multiplexer -- small, fast, but difficult fitting

– Crossbar -- easy fitting but large and slow

27

28

Problems with CPLDs• Pin locking

– Small changes, and certainly large ones, can cause the fitter to pick a different allocation of I/O blocks and pinout

– Locking too early may make the resulting circuit slower or not fit at all

• Running out of resources– Design may “blow up” if it doesn’t all fit on a single

device

– On-chip interconnect resources are much richer than off-chip

– Larger devices are exponentially more expensive

fplds

Education