1. EET 3350 Digital Systems Design
Textbook: John Wakerly
Chapter 9: 9-5
CPLDs
1
2. Agenda for Today
• Overview of FPLDs
– History
– Tradeoffs
• CPLDs
– General Description
– Basic Architecture
• Specific Vendor Devices
– Xilinx
– Altera
• Xilinx XC9500 Series
• CPLD Problems
2
3. Hierarchy of Logic Implementations
Logic
Standard
ASIC
Logic
today’s focus Programmable
Logic Devices Gate Cell-Based Full Custom
(FPLDs) Arrays ICs ICs
SPLDs CPLDs
(e.g., PALs) FPGAs
Acronyms Common Resources
SPLD = Simple Programmable Logic Device Configurable Logic Blocks (CLB)
PAL = Programmable Array Logic – Memory Look-Up Table (LUT)
CPLD = Complex PLD – AND-OR planes
– Simple gates
FPGA = Field Programmable Gate Array
Input / Output Blocks (IOB)
ASIC = Application Specific IC – Bidirectional, latches, inverters,
pullup/pulldowns
Interconnect or Routing
– Local, internal feedback, and global
3
4. Field-Programmable Logic Devices
• Component function is defined by user under program
control
• Logic Cells are interconnected by programming
• Advantages:
– Flexible design that changes by
reprogramming, ease of design
changes
– Reduce prototype-product time
– Large scale integration (over
100,000 gates)
– Reliability increased, low financial
risk
– Smaller device, low start-up cost
4
5. FPLD Capacities
• “Equivalent gates” refers
loosely to the number of two-
input NAND gates.
• The chart serves as a guide
for selecting a device for an
application according to the
logic capacity needed.
• Each type of FPLD is
inherently better suited for
some applications than for
others.
5
7. Which Implementation Technology?
• Economic versus technical factors
– The next few slides off a comparison of economic and
technical factors associated with these technologies
standard
components
CPLD Gate Std. Full
SSI/MSI SPLD
FPGA Array Cell Custom
semicustom
technologies
7
8. Comparison of Implementations
• The table below offers a comparison of the major
implementation technologies over four key factors
Gate Standard Full
SSI/MSI SPLD FPGA
Array Cell Custom
Gates/Component 5 - 100 50 - 5K 100 - 10K 500 - 100K 10K - 500K 100K - 10M
Cost/Gate
High Low
NRE Cost ($) - 1-2K 2-10K 5-50K 10-100K 50K-5M
Development time - 1-2 1-2 2-20 5-50 20-200
(weeks)
8
10. Evolution of Implementations
• CPLDs and FPGAs continue to evolve in parallel
‘standard
1960 components’
SSI ‘semicustom
components’
1970 MSI
Gate Array
Simple PLD
LSI Standard Cells
1980
VLSI CPLD FPGA
1990
2000
parallel
development
Today
10
11. 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
Programmable
Logic Devices
(FPLDs)
SPLDs CPLDs FPGAs
(e.g., PALs)
11
12. 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
Programmable
– A high ratio of flip-flops to logic resources Logic Devices
(FPLDs)
SPLDs CPLDs FPGAs
(e.g., PALs)
12
13. 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 Programmable
Logic Devices
(FPLDs)
SPLDs CPLDs FPGAs
(e.g., PALs)
13
14. SPLDs
• We have already taken a close
look at SPLDs
• A PLA-like SPLD is illustrated
at left
– PAL and GAL devices offered a
Logic Functions
somewhat better solution
• SPLDs are good alternative to
Sums
using SSI and MSI devices
– Especially if re-programmable
Programmable
Logic Devices
(FPLDs)
Product Terms
SPLDs CPLDs FPGAs
(e.g., PALs)
14
15. 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
• SPLDs have nearly replaced
TTL logic which was the Programmable
Logic Devices
dominate approach to logic (FPLDs)
implementation SPLDs CPLDs FPGAs
(e.g., PALs)
15
16. 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
Programmable
Logic Devices
(FPLDs)
SPLDs CPLDs FPGAs
(e.g., PALs)
16
17. 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
Programmable
Logic Devices
(FPLDs)
CPLD Architecture
SPLDs CPLDs FPGAs
(e.g., PALs)
17
18. 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
Programmable
Logic Devices
(FPLDs)
SPLDs CPLDs FPGAs
(e.g., PALs)
18
19. 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.
Programmable
Logic Devices
(FPLDs)
SPLDs CPLDs FPGAs
(e.g., PALs)
19
20. Complex PLDs
• Each manufacturer has a proprietary name for its
CPLD programming system
• For example, Lattice calls it "in-system programming"
• However, these proprietary systems are beginning to
give way to a standard from the Joint Test Action
Group (JTAG)
Programmable
Logic Devices
(FPLDs)
SPLDs CPLDs FPGAs
(e.g., PALs)
20
21. Complex PLDs versus FPGAs
• 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
Programmable
Logic Devices
(FPLDs)
SPLDs CPLDs FPGAs
(e.g., PALs)
21
22. 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
22
23. CPLD Architecture
• Generalized
architecture for a
complex PLD
• Programmable
Interconnect Array
– Capable of
connecting any LAB
input or output to any
other LAB
• Logic Array Blocks
– Complex SPLD-like
structure Programmable
Logic Devices
(FPLDs)
• Input/Output Blocks
SPLDs CPLDs FPGAs
(e.g., PALs)
23
24. CPLD Architecture
• Each of the SPLD-like blocks in
a CPLD can be programmed as
with a PAL or GAL
• Many SPLD-like blocks (e.g.,
LABs) are included in one CPLD
Feedback Outputs • LABs can be interconnected to
build larger logic systems
Programmable
Logic Devices
(FPLDs)
SPLDs CPLDs FPGAs
CPLD Architecture (e.g., PALs)
24
25. 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
Programmable
Logic Devices
(FPLDs)
SPLDs CPLDs FPGAs
(e.g., PALs)
25
26. 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).
• Performance of CPLDs is
usually better than FPGAs,
but depends on vendor,
number of cells in CPLD, and Programmable
Logic Devices
(FPLDs)
compared FPGA.
SPLDs CPLDs FPGAs
(e.g., PALs)
26
27. CPLDs
• The block diagram at
right for the Cypress
Semiconductor CPLD
(Ultra37128) illustrates
the general architecture
of CPLDs
Programmable
Logic Devices
(FPLDs)
SPLDs CPLDs FPGAs
(e.g., PALs)
27
28. Cypress Ultra 37000 Family
• In-system reprogrammable
CMOS CPLDs
– JTAG interface for
reconfigurability
– Design changes do not cause
pinout changes
– Design changes do not cause
timing changes
• High density
– 32 to 512 macrocells
– 32 to 264 I/O pins
– Five dedicated inputs including
four clock pins
28
29. Cypress Ultra 37000 Family
• Characteristics of devices in the Ultra 37000 Family
29
30. CPLDs
• Complex Programmable Logic Devices
– Contain from 10-1000 macrocells
– Each macrocell is equivalent to around 20 gates
– Support up to 200 I/O pins
• The key resource in a CPLD is the programmable
interconnect
– Tradeoff between space for macrocells and space for
interconnect
– Careful design will limit the connections between
macrocells
Programmable
Logic Devices
(FPLDs)
SPLDs CPLDs FPGAs
(e.g., PALs)
30
31. CPLD Architecture
• Complexity of CPLD is between FPGA and SPLD
LAB – Logic Array Block / uses PALs
PIA – Programmable Interconnect Array 31
32. CPLD Architecture
• Example Logic Array Block
Extra function (e.g., g,
h) i/ps for OR term 2:1 Mux
D-FF
PLA-like AND array
Literal inputs (e.g., a, b, c)
32
33. Programmable Interconnect Array
• Consists of connectors that run throughout the CPLD
to connect the macrocells in each LAB
• The PIA also connects the AND gate and other
elements of the macrocells
33
35. 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
XC9500
CPLD
Series
35
36. Typical CPLD Packages
• CPLDs are made using 2 to 64 SPLDs
• Packages use 44-pins to over 200-pins (or more)
36
37. 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
37
38. 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
38
39. 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
39
41. XC9572 CPLD Datasheet
• XC9572 CPLD from Xilinx
• 7.5 ns pin-to-pin logic
delays on all pins
• 72 macrocells with 1,600
usable gates
• Up to 72 user I/O pins
• Four 36V18 Function
Blocks
• Available in 44-pin PLCC,
84-pin PLCC, 100-pin
PQFP and 100-pin TQFP
packages
41
42. XC9572 CPLD Packages
• XC9572 pinout for the 84-pin PLCC package and
photo of the 100-pin TQFP package
84-pin PLCC 100-pin TQFP
(pin 1)
42
43. XC9572 CPLD Part Numbers
• The part number for Xilinx CPLD devices includes
information as follows:
43
44. 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.
44
45. 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
45
46. 9500-Series Macrocell
• 18 macrocells per Function Block
Set control
Programmable inversion
or XOR product term
Up to 5 product terms
Global clock or product-term clock
Reset control
OE control
46
48. XC9500 Family
• 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.
48
49. 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.
49
50. XC95108 CPLD Datasheet
• XC95108 shares the
characteristics of all other
XC9500 series devices
• 108 macrocells with 2400
usable gates
• Up to 108 user I/O pins
• Six 36V18 Function Blocks
• 10,000 program/erase
cycles
• Available in 84-pin PLCC,
100-pin PQFP, 100-pin
TQFP and 160-pin PQFP
packages
50
51. XC95108 CPLD Datasheet
• XC95108 block diagram
is similar to all of the
others in the XC9500
family
51
52. 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
52
53. 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
53
A designer may use any technology to implement a design – normally the decision is dictated by economic factors
Rather than try to draw any hard-and-fast comparisons between the costs of different implementation techniques, it is more instructive to examine here the relationship between the 'start-up' and 'high-volume' costs of the different techniques, when a family of curves of the form given below may be constructed, showing that the most economic form of implementation depends upon the volume of devices to be used.
Note that for any given volume, one technology will offer the lowest cost… For successive choices, the silicon utilisation is more efficient (and so unit costs are lower), but the initial cost in terms of design time, CAD facilities and manufacturing are higher.
Standard = ‘fixed function’ What’s the difference between ‘standard’ and ‘custom’ components? (If you sell enough custom chips they become standard…) ‘ Custom’ relates to the layout procedure ‘ Semicustom’ technologies allow the economies of mass production with the ability to customise a device for a specific application. Also known as ‘ASICs’.
