Cypress FR81S CY91F52 Series Operating instructions

www.cypress.com Document No. 002-09375 Rev. *B 1
AN209375
Recommendation for Hardware Setup 32-Bit FR81S Family
This application note describes how to set up a hardware environment for Cypress FR81S MCUs. As an example, the
CY91F52x MCU is used.
Contents
1Introduction..................................................................1
2Minimal System...........................................................2
2.1 Schematic...........................................................2
2.2 Serial Interface....................................................2
2.3 Power supply ......................................................2
2.4 Analog Digital Converter Supply Pins.................2
2.5 Analog Input Pins................................................3
2.6 Reset Pin (RSTX) ...............................................4
2.7 Non maskable Interrupt Pin (NMIX)....................4
2.8 C-Pin...................................................................5
2.9 Clock Source.......................................................5
2.10 Mode Pins...........................................................6
2.11 Not Connected Pins............................................6
2.12 Debug Interface connection................................7
3Layout and Electromagnetic Compatibility...................8
3.1 General...............................................................8
3.2 Power supply Pins ..............................................8
3.3 Oscillator Pins.....................................................9
3.4 Power Line Routing.............................................9
3.5 Power Supply Decoupling.................................10
3.6 Recommended Power Supply Circuit ...............12
3.7 Reset circuit......................................................13
3.8 Quartz Crystal Placement and Signal Routing..16
3.9 Test points........................................................18
3.10 Other documents ..............................................18
4Port Input / Unused Pins / Latch-up...........................19
4.1 Port Input / Unused Pins...................................19
4.2 Latch-up consideration (switch) ........................20
4.3 5 V Tolerant Input pins......................................24
5Flash Programming Connection................................25
5.1 Overview...........................................................25
5.2 Serial programming via UART0........................25
5.3 Serial programming via MDI interface...............27
5.4 Parallel programming interface.........................29
5.5 Security function ...............................................29
6Reset Behavior of IO port pins ..................................30
7Additional Information................................................30
Worldwide Sales and Design Support.............................32
Cypress Developer Community.......................................32
Technical Support...........................................................32
1 Introduction
This design guide describes design restrictions and recommendations regarding signal wiring and the electrical power
system of the MCU. For more details about the device features and its relevant settings, please refer to the FR81S
Hardware Manual and its corresponding Datasheet for electrical characteristics.

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2 Minimal System
This chapter gives an example for a minimum hardware system.
2.1 Schematic
The following graphic shows a schematic of a minimum hardware system. Note that for other MCU families a different
pinning is needed.
Figure 1. Principal Schematic for Minimal Requirements
*1 only needed for dual clock devices.
*2 please refer to chapter 3.6 Recommended Power Supply Circuit.
2.2 Serial Interface
The “PC connection” section is only needed, if no 5 V external serial data lines for programming exist. The MAX232 is
a standard level shifter, which converts the 5 V levels of the MCU to ±12V RS232V24 levels and vice versa.
If you use a 3.3 V system a MAX3232 is recommended.
Please consider, that the internal charge pumps of the level shifter can produce noise on the +5 Volts line, which can
influence the ADC, if AVCCn and AVRHn are directly (unfiltered) connected to it.
2.3 Power supply
The power supply should be from 2.7 Volts to 5.5 Volts for normal usage. If a different supply voltage is used please
refer to the corresponding data sheet.
2.4 Analog Digital Converter Supply Pins
The analog converter supply pins (AVCCn, AVRHn / AVRLn, AVSSn) should be connected even if the ADC of the MCU
is not used. Please refer to our application note “mcu-an-300215-e-16fx_adc” for using the ADC and pin connection.

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2.5 Analog Input Pins
Because the ADC works with an internal sample capacitor (Cadc) you must be aware of the time needed to fully charge
this capacitor to the corresponding analog signal source voltage level by the end of the sample time.
When the external impedance is too high, the sampling period for analog voltages may not be sufficient. In this case, it
is recommended to connect an external capacitor (Cext, approx. 0.1 μF) to the analog input pin.
An input impedance maximum (Rext) 15k Ohm is recommended. So, an appropriate sample time has to be selected
depending on the impedance Rext and the capacitance Cext.
Please refer to Datasheet “A/D Converter” chapter for further information.
Figure 2. Analog Input Circuit Model
AN1 pin
Rext
Analog
Signal
Source #1 Cext
AN2 pin
Rext
Analog
Signal
Source #2 Cext
ANn pin
Rext
Analog
Signal
Source #n Cext
Cpad
Cpad
Cpad
Analog SW (Closed during sample)
Analog SW
Analog SW
Radc
Cadc
ADC
MCU
Table 1. Reference Values
Component
Value
AVcc
Cadc
8.30 pF (Max)
4.5 V… 5.5 V
Cadc
8.30 pF (Max)
3 V… 3.6 V
Radc
1.9K (Max)
4.5 V… 5.5 V
Radc
4.3K (Max)
3 V… 3.6 V
Cpin
5pF..15pF

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2.6 Reset Pin (RSTX)
To reset the MCU a switch connects this pin to Vss (Ground). There is internal 50k pull-up resistor, but for high noise
requirements an external pull-up resistor with typical 10k is recommended. Additionally, a capacitor has to be connected
between Vss and the reset pin for debouncing the switch and for EMI protection. From experience a capacity of not
more than 1 nF is recommended. This capacity covers the most common frequency protection in a wide range. Higher
capacities and high impedance may cause latch-up effects together with an RSTX-Switch and low EMI protection. The
reset level of RSTX pins depends on the logical level on NMIX pin. Please refer to Hardware manual chapter 7 Reset.
Table 2. RSTX and NMIX Function
RSTX
NMIX
Function
1
1
Normal operation
1
0
Non maskable interrupt
0
1
External reset Reset (RST) Synchronous reset factor
0
0
Irregular reset Initialize reset (INIT) Asynchronous reset factor
(not guarantee that memory contents have not been destroyed by the reset)
2.7 Non maskable Interrupt Pin (NMIX)
The NMIX supports two several functions, (a) using as NMI input and (b) simultaneous assert of RSTX and NMIX pins
to generate an irregular reset. There is internal 50k pull-up resistor, but for high noise requirements an external pull-up
resistor with typical 10k is recommended.

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2.8 C-Pin
A 4.7 µF ceramic capacitor (dielectric X7R) must be connected very close to the C pin of the MCU. Furthermore, an
additional 100 nF (dielectric X7R) for higher noise frequencies is recommended. Otherwise the MCU may not operate
correct or will be damaged in worst case. Please refer to Datasheet chapter “Recommended operating conditions” for
further information.
Figure 3. Internal Voltage Regulator and C Pin
MCU GPIO GPIO GPIO
GPIOGPIOGPIOGPIO
GPIO GPIO GPIO
GPIOOSCGPIO
Vcc Vcc 5V
Vcc
Vss
GND
Vss
GND
5V
5V
5V
GND
Vss
GND
Vcc Vss
C
Internal 1.2V
Vss
GND
4.7µF
(ceramic X7R)
CORE
internal
voltage
regulator
*1 Note *1 : Vss pin
closest to C pin
2.9 Clock Source
A clock source must be provided to the MCU. Therefore, crystals or external clock signals can be used. For external
source pin X0 (X0A) is used whereby pin X1 (X1A) is not connected.
There are MCU derivatives for dual clock and single clock devices, the sub clock can be enabled by software. If sub
clock X0A pin is neither used as GPIO nor as clock input, the pin can be left open.
If you want to use only CR clock, then you need a MCU version with disabled CSV.
Please also refer to the chapter “Handling the device” in the corresponding hardware manual for details.

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2.10 Mode Pins
The mode pins set the current operation mode for the MCU. For a minimal system, only two modes are necessary:
Flash-Asynchronous-Serial-Programming-Mode and Run Mode.
In the case, you use the Serial Programming Mode the MD-pins need pull-up/pull-down resistors (typically 2k7
resistors). In order to increase the protection against ESD and EMI effects the PCB tracks should be as short as
possible.
If the Serial Programming Mode is not used the MD-pins can be connected directly to Vcc or GND. Please refer to
Datasheet chapter “Handling devices” for further information.
The following settings are used for the both modes mentioned above:
Table 3. Mode Pin Settings (x: does not care)
Mode
P006
MD0
MD1
Serial Programming Mode
1
0
1
Run (Internal Vector Mode)
x
1
0
2.11 Not Connected Pins
In default state after power-on reset usually the GPIO pins are in high-z state.
If unused input pins are left open, they may cause a permanent damage to the device due to malfunction or latch-up.
Connect at least a 2k resistor to each unused pin in pull-up or pull-down configuration. Also, if I/O pins are not used,
they must be set to the output state for releasing or they must be set to the input state and treated in the same way as
for the input pins.
Concerning special use cases, it is referred to Port Input / Unused Pins / Latch-up for how to proceed with unused (not
connected) pins.

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2.12 Debug Interface connection
Debugging is only supported by the 50 Ohm single-wire debug system, which is shared with mode pin ‘DEBUGIF’.
Concerning current limitation by an external resistor on programming tool side and maximum clamping current/structure
at the ‘DEBUGIF’ pin specified values must be taken out of data sheet.
Figure 4. How to connect Debug System with Programming Connector
VCC
Debug
Connector R1
ECU
GND
R2
D2
DEBUGIF
MCU
D1
L1L2
GND
(R1 = 43 R, R2 = 10 k, D1 e.g. HZM6.2Z4MFA-E, D2 schottky diode e.g. BAS40, Debug connector: SMA 50R connector
for development target boards.)
Table 4. SPEED-BOX General Specifications
Item
Specification
MDI bus maximum communication speed
(from MCU to SPEED-BOX)
50 Mbps
Does not depend on cable* length.
(* cable between SPEED-BOX and ECU)
MDI bus maximum communication speed
(from SPEED-BOX to MCU)
Cable* length 2 m or less : 25 Mbps
Cable* length 5 m or less : 12.5 Mbps
Cable* length 10 m or less : 6.25 Mbps
(* cable between SPEED-BOX and ECU)
L1 wiring length
As short as possible, keep less than 5 cm.
L2 wiring length
Less than 15 cm.
Please check for detailed OCDS layout design rules of the
MB2100-01-E (see chapter Flash Programming Connection)
and the chapter ‘On Chip Debugger: OCD’ of the hardware
manual.

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3 Layout and Electromagnetic Compatibility
This chapter gives some tips for layout design.
3.1 General
To avoid ESD problems and noise emission of the system some rules for the layout design have to be observed.
The most critical point is the C pin because this is the connection to the internal 1.2 V supply for the MCU core. Thus,
two decoupling capacitors have to be placed very near to this pin.
Also, the ground and Vcc routing has to be done carefully. Vcc lines should be routed in star shape. We recommend a
Vss ground plane on the mounting side just under the MCU. For both Vcc and Vss only one connection to the rest of
the circuit should be done, otherwise noise is carried-over from and to the MCU. This one connection should be used
for power supply filtering (PI-Filter with ferrite). Decoupling capacitors (DeCaps) have to be placed as near as possible
to the related pins. If they are placed too far away, their functionality becomes useless.
If possible all decoupling capacitors should be placed on the same mounting side as the MCU; otherwise the DeCaps
could be placed on bottom layer below the MCU.
PI-Filter prevents EMI from radiating from power supply planes. Keep maximum distance between IN and OUT
capacitor to avoid noise coupling at PI-Filter.
If crystals are used, they have to be placed as near as possible to the X1(A) pins, output of the inverter. The feedback
resistor of oscillator circuit (typ. 1Mohm) is already implemented internally. The evaluation of crystal/resonator and load
capacitor must be tested by the related crystal vendor by crystal matching test.
3.2 Power supply Pins
The following table shows the EMC critical pins and gives short information about how to connect them.
Table 5. Power Supply pins in use
Pin Name
Function
VCC
Dedicated power supply pins for IO buffer and crystal oscillator.
VCC5*
*Only for CY91570/590 series.
Dedicated power supply pins for IO buffer and crystal oscillator.
VCC3*
*Only for CY91590 series.
Power supply pins for 3V3 IO buffer.
VCCE*
*Only for CY91570 series.
Power supply pins for 3V3 IO buffer.
DVCC*, DVSS*
*Only for CY91570/590 series.
Power supply pins for high current output buffer pins.
VSS
Dedicated power supply (0 V) pins. (IO buffer, MCU core and crystal oscillator)
AVCCn
Dedicated power supply pins for the AD-converter (unit n).
AVRHn / AVRLn
Dedicated positive/negative reference voltage pin for the AD-converter (unit n).
AVSSn
Dedicated power supply pin (0 V) for the AD-converter (unit n).
C
Dedicated power supply pin for the internal power supply regulator (used to supply the
MCU core). External capacitor connected to this pin is required.
C_1*, C_2*, C_3*
*Only for CY91590 series.
Dedicated power supply pins for the internal power supply regulator (used to supply the
MCU core). External capacitors connected to these pins are required. Please refer to
datasheet “C Pin Connection Diagram” reference for further information.

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3.3 Oscillator Pins
The following table shows the oscillator pins and gives short information about how to connect them.
Table 6. Oscillator pins in use
Pin Name
Function
X0, X0A
Oscillator input, if not used so shall be connected with pull-up or pull-down resistor (see please
DS)
X1*, X1A*
*Only for devices with subclk.
Oscillator output, the crystal and load capacitor must be connected with shortest distance and
without any vias.
If not used so shall be open
3.4 Power Line Routing
In general, the Vcc and Vss lines should not be routed in “chains”, but in “star shape”. For two layers board the Vss is
recommended as ground plane which covers the chip package, and is connected in one point to Vss of the whole circuit
to avoid a ground loop.
Below is a principal example of a bad and a good power line routing:
Figure 5. Example of bad vs. good power line routing
For four and more layers PCB the Vcc and Vss should be routed as a plane in the inner layers of PCB. Concerning the
layer stack the several Vdd power supply planes should be not overlapped in parallel layers to avoid noise coupling.
Recommendation for good EMC behaviour:
▪Use four layers or six layers PCB
▪Use power supply planes (ground and power) in the inner-layer of PCB layer stack
▪Reduce the distance between the power planes (low impedance)
▪One or two decoupling capacitors close to each VCC pad/pair to adjacent VSS-pad/pair (route under).
▪Use capacitor groups to match frequency behaviour of power supply decoupling. The decoupling capacitors can
have values between 1 nF and 10 µF.
▪Use ferrite filter for each power domain
▪Split the used I/O signals in separate layer for low / high speed, and digital / analog signal types

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Below is an example for PCB layer stack:
Figure 6. Example of PCB layer stack
GND
AVcc
Vcc
low speed signals
high speed signals
BAD crosstalk between
different power supply
planes
GND
Avcc / Vcc
low speed signals
high speed signals
GOOD separation of
power supply planes for
low EMC requirements
3.5 Power Supply Decoupling
DeCaps for power supply have to be placed within the “current flow”. Otherwise they are senseless, because then their
function become inoperable. The following graphic illustrates this:
Figure 7. Power Supply decoupling caps placement

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Usually the noise current should flows thought the soldering pad of decoupling capacitor CB. The following routing and
placement for single-side assembled boards is recommended:
Figure 8. Power Supply decoupling on single-side assembled boards
L4
L3 (VCC)
L2 (GND)
L1 (MCU)
VCC
VSS MCU
CB
The following routing and placement for multi-layer PCB is recommended. Note that despite the capacitor is placed on
the opposite side as the MCU, this solution is the best for high-density board assembly.
Figure 9. Power Supply decoupling on double-side assembled boards
L4
L3 (VCC)
L2 (GND)
L1 (MCU)
VCC
VSS MCU
L1 (MCU)
L2 (GND)
L3 (VCC)
L4
CB

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3.6 Recommended Power Supply Circuit
To meet EMC requirements for the target board, a noiseless supply is necessary. Therefore, the supply should be
filtered as shown in Figure 10. Switched IO pins like stepper motor controller or external bus interface can generate
spikes on the supplies. These are difficult to filter using capacitors only. A series inductor (ferrite, e.g. WE742792022)
is therefore recommended, as shown.
Figure 10. Principal Supply circuit
L
10uF
GND
MCU
AVcc
Vcc
VSS
GND
AVSS
5V
10uF
GND
GND
100nF
X7R
Vcc
L
10uF
GND
5V
10uF
GND
Close to
MCU pins
AVRH
R2*
*R2 (e.g. 10R) : Optional
GND
GND
100nF
X7R
GND
C*
C*
GND
100nF
X7R
GND
GND
100nF
X7R
GND
C*
C*
*C (e.g. 1nF) : Optional

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3.7 Reset circuit
All hard reset events are extended by the hard reset extension circuit to guarantee the stabilization of the Low Voltage
Detector (LVD) and complete reset of the device before program execution starts. The reset signal at RSTX pin goes
through a noise filter to avoid any spike on the reset input. Please note there are two types of reset level (RST and
INIT).
Figure 11. Block Diagram of reset extension circuit

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Please see also the datasheet, chapter “External reset timing” of related MCU series.
Table 7. External reset timing
Figure 12. External reset timing

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Figure 13. Block Diagram of reset extension circuit

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3.8 Quartz Crystal Placement and Signal Routing
The feedback resistor (Rf) of the oscillator circuit is already inside of MCU device. The value of both load capacitors
(C1, C2) should be determined with crystal matching test. The crystal matching test must be done by the crystal
manufacturer based on the target board. As a result of crystal test maybe will be needed a damping resistor (Rd).
Figure 14. Principal Oscillator Circuit
X0
X1
4MHz
10p
CY91F52x
C1
10pC2
Rd
0R
Rf
Inverter
Vss
Figure 15. Principal Oscillator Circuit and Startup Sequence

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As you can see in Figure 16 the routing of these components is very important in order to reduce EMI effects. These
components have to be placed on the same layer as the MCU. The connection of C1 and C2 to the Vss pin must be
routed in a star way and so close as possible. The only vias should be placed to connect this ground star routing to the
ground plane in other layer, never use vias to connect these components with the corresponding MCU pins.
Figure 16. Layout example for crystal oscillator circuit
DeCap CB
on backside
Vias to Vcc plane
on inner layers
Vias to ground plane
on inner layers
Ground plane on
inner layers
X0
Vcc
Vss
CB
SMD
Quartz Crystal
C1
C2
X1
Rd
Figure 17. Stray capacitance of PCB
X0
X1
4MHz
CY91F52x
C1
C2 Rd
0R
Rf
Inverter
C3*
C4* C3*,C4* : Stray
capacitance of PCB
)()( )()(
4231
4231 CCCC CCCC
CL


Equation: CLcalculation with stray capacitance of PCB.
For a proper performance of the oscillator circuit it is necessary to match the load capacitors (C1, C2) with the crystal
when the MCU, PCB or crystal are replaced for a different one.
As a result of this matching test the value of CLis provided and then the calculation of C1and C2can be done using
the Equation.

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3.9 Test points
The FR81S devices support several clock output functions for failure analysis in development, mass production or in
the field. MONCLK out could be used e.g. for clock calibration of main or sub oscillator.
Figure 18. MONCLK internal clock select and prescaler
Table 8. Supported output functions for test purposes
3.10 Other documents
For further detailed information please refer to the application notes on the web page.

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4 Port Input / Unused Pins / Latch-up
How to connect input port pins and how to proceed with unused pins
4.1 Port Input / Unused Pins
It is strongly recommended not to leave Input Pins unconnected. In this case those pins can enter a so-called floating
state. This can cause a high ICC current, which is adverse to low power modes. Also damage of the MCU can happen.
Use the internal pull-up/down resistors, if the port provides such function. If not, use external pull-up or pull-down
resistors to define the input-level. If both solutions are not possible, set the Port Pin to Output.
Never connect a potential divider with almost same resistor values.
Figure 19. Principle using of input circuit to avoid latch-up or leak current
Be careful with connection of input pins to other devices, which can go into High-Z states. Always use pull-up or
pull-down resistors in this case.
Outputs from external circuits should always be connected via a serial resistor to a MCU input pin.
Debouncing and decoupling capacitors should always be chosen as smallest as possible. Please refer to Latch-up
consideration (switch).
All pins are set to input Hi-Z after its power-on default. Therefore set unused pins to input with internal pull-up/down
resistor, or provide them with pull-up or pull-down resistors.

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Do not connect any input ports directly to VCC or VSS (GND)! Always use pull up or down resistors (2k … 10k Ohms).
If available, it is possible to use the internal pull up or pull down resistors as well. Please note the value internal resistors
can be 20k … 100k depends on the device and temperature.
4.2 Latch-up consideration (switch)
Be careful with external switches to VCC or ground together with debouncing capacitors connected to port pins.
A usual configuration is shown in the following schematic:
Figure 20. Usual Configuration Switch
RPD is a pull-down resistor and CBD a debouncing capacitor. If the switch SW is open, a “0” is read from the port pin
Pxy. If the switch is closed the input changes to “1”.
From the physical aspect, it has to be considered, that the switch is often placed in distance to the MCU by cable, wire,
or circuit path. The longer the circuit path is the higher will be its inductivity LX (and capacity CX).
An equivalent circuit diagram looks like the following illustration:
Figure 21. Usual Configuration Switch, equivalent circuit