Hardware Checklist There is also the Hardware Design Checklist for the Blackfin® Processors. General Hardware Problems The following sections address design issues not associated with memory interfaces or specific peripherals. NMI Polarity Double-check the polarity of the Non-Maskable Interrupt (NMI (Non-Maskable Interrupt)) signal for the processor being used. On several Blackfin processors (the ADSP (Analog Digital Signal Processor)-BF531/BF532/BF533/BF535 and the ADSP (Analog Digital Signal Processor)-BF561), the NMI (Non-Maskable Interrupt) signal is active high. On all the other Blackfin processors, the NMI (Non-Maskable Interrupt) signal is active low in order to better connect to standard Supervisory parts. Remember that if the NMI (Non-Maskable Interrupt) signal is not used, it should be tied to its inactive state. Do not let the NMI (Non-Maskable Interrupt) signal float, and do not tie it to its active state. Five-Volt Tolerance Applying five volts to signals that are not rated for this potential can damage the device and cause malfunction. Blackfin processor outputs should not be connected to the inputs of five-volt devices. Most Blackfin processor signals cannot tolerate five volts. There are a few exceptions, such as some of the Two-Wire Interface (TWI (Two Wire Interface (I2C-compatible))) signals. Level shifters are required on all other processor signals to keep the signal voltage at or below absolute maximum ratings as defined in the specific Blackfin processor data sheet. Level shifters are commonly required for CAN (Controller Area Network - common automotive serial bus) transceivers and the ATAPI (Advanced Technology Attachment Packet Interface (hard drives!)) interface. Current-limiting resistors do not provide sufficient protection against high voltage. Unused Signals Check the end of the signal list description section of the data sheet to see what to do with unused signals. In general, the need to terminate unused signals has been eliminated, but the signals that require termination can be found in the data sheet. Failure to connect unused signals such as /NMI (Non-Maskable Interrupt), NMI (Non-Maskable Interrupt) or /BR may cause symptoms that appear to be power sequence or reset problems. Applications requiring high EMC susceptibility / immunity may terminate all unused signals, if desired. Signal Integrity Rapid rise-time and fall-time of signals is a primary cause of signal integrity issues such as intermittent communication failure. The edge rates on the Blackfin processor differ from signal to signal. Likewise, some signals have greater sensitivity to noise and reflections than other signals. Use simple signal integrity methods to prevent transmission-line reflections that may cause extraneous clock and sync signals. Short trace length and series termination are critical for the following signals: CLKIN signals should have impedance matching series resistance at the driver SPORT (synchronous high speed serial port) interface signals (TCLK, RCLK, RFS, and TFS) should use termination PPI (Parallel Peripheral Interface) signals, such as PPI (Parallel Peripheral Interface)_CLK and Sync signals, also benefit from these standard signal integrity techniques SDRAM (synchronous dynamic random access memory (system memory)) clocks, control, address, and data can benefit from series termination that also reduces unwanted EMI In cases where signals have multiple sources, it will be difficult to keep the traces short, and simulation may be appropriate. IBIS models that can assist with signal simulation are available from the Analog Devices web site. Some new and future Blackfin processor family members will support additional signal integrity features such as programmable input hysteresis or programmable output drive strength. Consult the appropriate hardware reference manual for details. Test Points and Signal Access The debug process can be aided by adding test points on signals such as CLKOUT or SCLK (System Clock), bank selects, PPI (Parallel Peripheral Interface)_CLK, and /RESET. If selection inputs such as Boot Mode (BMODE) are connected directly to power or ground, they will be inaccessible under a BGA-package chip. For debugging, it is helpful to use pull-up and pull-down resistors instead of tying inputs directly to power or ground. Bypass Capacitors Appropriate bypass capacitors on the internal power supply become critical at higher operating speeds. Unwanted parasitic inductance in capacitors and traces reduces the effectiveness at high frequency. Two things are needed when processors operate above 100 MHz (Megahertz). First, capacitors should be physically small and their leads should be short to reduce inductance. Surface mounted capacitors of size 0402 will yield better results than larger sizes. Second, lower values of capacitance will raise the resonant frequency of the LC circuit. Although several 0.1 uF capacitors work well below 50 MHz (Megahertz), a mix of 0.1, 0.01, 0.001 uF and even 100 pF is preferred in the 500 MHz (Megahertz) range for VDDINT. Driving /RESET The inputs of most Blackfin processors have no hysteresis, thus, they require a monotonic rise and fall. Therefore, even the /RESET signal should not be connected directly to an R/C time delay because such a circuit would be noise sensitive. Instead, /RESET should be provided through a reset supervisory chip. Board to Board Communications Some communication standards such as CAN (Controller Area Network - common automotive serial bus) and TWI (Two Wire Interface (I2C-compatible)) have special requirements when unpowered. For example, an unpowered pull-up resistor may cause excessive leakage, thereby disrupting communication between other units on the bus. This unpowered situation is a common consideration in ‘hot swap’ applications. JTAG The Blackfin processor JTAG (Joint Test Action Group - low level interface to cpu) reset pin, /TRST, should be pulled down in normal operation. An application note is dedicated entirely to considerations for JTAG (Joint Test Action Group - low level interface to cpu) connections. Refer to Analog Devices JTAG (Joint Test Action Group - low level interface to cpu) Emulation Technical Reference (EE-68)[1] for details. GPIO Port Signals Used as Inputs and Outputs At power-on reset, all general purpose signals are inputs. During the boot process, some of these signals may change to outputs, depending on the selected boot mode. For parts with HWAIT, this signal is an output for all boot modes. Output signals should not be used as inputs when driven by an external device. HWAIT should not be used as an output if the value is critical during the booting phase of operation. GPIO (General Purpose Input/Output) signals used as outputs should have pull-up or pull-down resistors to determine their state after reset. Outputs to be considered here include device enables (such as NAND (Not AND (large flash memory type)) flash) and communication handshake signals. Some examples are HWAIT, UARTxTX, UARTxRTS, CANxTX, SPI (Serial Peripheral Interface) slave-select inputs and outputs, serial TWI (Two Wire Interface (I2C-compatible)), and all chip select signals. Some general-purpose outputs that can be used at 5 V like SDA and SCL are open-drain in all modes. These are listed in the datasheet and require pull-ups to function as a general-purpose output. Signal capacitance may limit the output speed of these signals. Using EZ-KIT Lite® Schematics The EZ-KIT Lite evaluation system schematics are a good starting reference. Because the EZ-KIT Lite board is for evaluation and development, extra circuitry is provided in some cases. Read the EZ-KIT Lite board schematic carefully because sometimes a component is not populated and sometimes extra components have been added to make it easier to modify or measure. Asynchronous Memory Bus Request The Bus Request signal (/BR) requires a pull-up resistor in all designs. Erroneous bus requests will prevent bus operation if this signal is not pulled up or driven by an external device. Asynchronous Bus / GPIO Signal Muxing Considerations Asynchronous bus signals may be multiplexed with GPIO (General Purpose Input/Output) functions on some Blackfin processors. This may require the bus request GPIO (General Purpose Input/Output) to be programmed as bus request and require that GPIO (General Purpose Input/Output) be connected to a pull-up, as described above. As shown in the signal description, some processors allow some unused bus signals to be used as general-purpose input/output signals. However, if the asynchronous bus is used for booting, all address signals will be driven. Also, on some processors, /BG and /BGH will be driven during the boot process and /BR is used as an input. This occurs when BMODE is set to parallel memory or, for processors featuring One-Time Programmable (OTP (One Time Programmable (memory))) memory, when the asynchronous bus is enabled by OTP (One Time Programmable (memory)) programming. Other processors share other asynchronous bus signals with GPIO (General Purpose Input/Output). Consult the booting section of the hardware reference manual for details. 8/16-Bit Memories Remember to use the proper addresses to connect to 8-bit memory on the ASYNC memory banks. Because there is no true byte addressing to external memory, 8-bit memory is addressed the same as 16-bit memory. Use A1 (not /ABE0 or /ABE1) as the LSB of the address. 16-bit memory with byte enable signals can be accessed 8 bits at a time. Otherwise, 16-bit memories are word wide only. Blackfin devices with a 32-bit EBIU (External Bus Interface Unit) can be programmed to connect with 16-bit memory, using /ABE3 as the least significant address of the external device. Refer to the processor's hardware reference manual for more information. ARDY If not used, ARDY can be terminated. In addition, ARDY can also be programmed to be ignored via software. If ARDY is used, consult the hardware reference manual. Some Blackfin devices require the ARDY input to be synchronous to SCLK (System Clock) (CLKOUT). Hibernate Considerations The datasheet may indicate that all external signals are tristate during hibernate. This includes bus strobes. Pull-up resistors are required on peripheral chip selects such as /AMSx. Other External Bus Interface Control Signals Although not required, pull-up resistors should be considered for all active low bus control signals to guarantee their state during power up and power down. Future Blackfin family members may have many device control signals multiplexed with GPIO (General Purpose Input/Output) and other functions. These may require pull-up resistors to prevent data corruption and bus contention during reset and prior to configuration. SDRAM Memory SDRAM Bank Addressing Use ADDR18 to connect to BA0. Use ADDR19 to connect to BA1. SDRAM Address SA10 Use SA10 to directly connect to A10 of the SDRAM (synchronous dynamic random access memory (system memory)) device. SA10 replaces the Blackfin processor’s ADDRx, based on whether a 16- or 32- bit (for 32-bit-wide external memory interface derivatives) device is connected to the SDRAM (synchronous dynamic random access memory (system memory)) interface. As an example, for an ADSP (Analog Digital Signal Processor)-BF561 Blackfin processor, SA10 replaces ADDR11 when a 16-bit SDRAM (synchronous dynamic random access memory (system memory)) device is used, and SA10 replaces ADDR12 when a 32-bit device is used. On the ADSP (Analog Digital Signal Processor)-BF533 Blackfin processor, SA10 replaces ADDR11. Note that the replaced ADDRx signal is not used. Therefore, the next higher processor address is connected to A11 of the memory. Refer to the “SDRAM Address Mapping” section of the hardware reference manual for details. Hibernate Considerations A pull-up resistor is recommended on /SMS. Synchronous DDR Memory DDR PCB Layout Proper PCB layout is a requirement of any DDR (Double Data Rate (memory)) memory design. Review the AC timing and specifications listed in the processor datasheet. Signal timing is a combination of device timing and the characteristics of the printed circuit board. Trace length difference, cross-talk, and voltage change may account for 300 to 500 ps of timing error. Follow the layout recommendations given by the memory manufacturer. Of critical importance is the reduction of DQS0 to DQ0-7 skew and DQS1 to DQ8-15 skew. The amount of allowed skew can be improved with the use of fast speed grade memory. Use careful trace length matching and increased spacing to reduce crosstalk. Serpentine traces should have a spacing of four times the trace width to provide sufficient delay. The trace length for the DCLK0- 1, DQS0-1, DQM0-1 and DQ0-15 signals should be less than 3.5 inches. DDR (Double Data Rate (memory))_VSSR should be connected directly to ground at the processor. DDR (Double Data Rate (memory))_VREF should be a low-impedance 30 mil wide connection. DDR Termination Use series termination on all data, address and control signals for up to four memory devices. Hibernate Considerations Pull-up resistors are recommended on the /DDRCS chip selects. Synchronous Burst Flash Memory Some Blackfin family members can attach directly to burst mode and page access mode flash devices. Care must be taken if the device functions as a boot source. If the Blackfin processor resets itself by a software reset command or watchdog timer event, the processor and memory may then operate in incompatible access modes. Use the OTP (One Time Programmable (memory))_RESETOUT_HWAIT feature to instruct the processor to configure the flash device before reboot. Consult the hardware reference manual and datasheet for booting, timing and connectivity information. Hibernate Considerations Pull-ups are required on peripheral chip selects such as /AMSx. SPI Interface Booting SPI (Serial Peripheral Interface) Master Boot mode requires a pull-up resistor on the GPIO (General Purpose Input/Output) signal used as the chip-select for the SPI (Serial Peripheral Interface) memory device. The name of the chip-select changes from one Blackfin processor to another. Check the SPI (Serial Peripheral Interface) booting section of the Blackfin processor's data sheet to find the SPI (Serial Peripheral Interface) /CS connection for booting. Most current processors require a pull-up resistor on MISO. In all SPI (Serial Peripheral Interface) systems, SPI (Serial Peripheral Interface)_SCK is best used with a pull-down resistor to define the initial state and to reduce noise. Also, refer to the “SPI Master Booting” section of the application note ADSP (Analog Digital Signal Processor)-BF533 Blackfin Booting Process (EE-240). MOSI and MISO The SPI (Serial Peripheral Interface) interface requires that all MOSI signals are tied together and all MISO signals are tied together. To prevent contention and possible damage to the device, double-check that these signals have not been interchanged. Connect MISO to MISO and MOSI to MOSI. If the peripheral signal names are DIN or DOUT, connect them according to their master or slave function. Proper schematic signal names will reduce confusion. Two-Wire Interface The Two-Wire Interface is an I2C (Inter-Integrated Circuit)-compatible peripheral. Because SCL and SDA are open drain outputs, both TWI (Two Wire Interface (I2C-compatible)) signals need pull-up resistors just like the I2C (Inter-Integrated Circuit) standard requires them. SD/SDIO Interface The Secure Digital (SDIO (Secure Digital Input Output)) interface is designed such that it requires no external pull-ups or pull-downs in most applications. SD (Secure Digital)/MMC (Multi Media Card) cards may require a weak pull-up on SD (Secure Digital)_CMD. Other resistor functions are provided internal to the processor. However, impedance-matching series termination resistors should be added on all signals. Consult the SD (Secure Digital) specification and the timing numbers in the datasheet to determine the maximum frequency for supporting both standard and high-speed SD (Secure Digital) devices. Also consider the time of flight if the SD (Secure Digital) connector is located remotely. SPORT Interface SPORTs in multi-channel mode that master the clocks and frame syncs should not connect TFS to RFS. In this mode, the TFS frames the active transmit channel data in the role of a Transmit Data Valid (TDV) signal. Clock Input Signals CLKIN The clock input to the Blackfin processor should start toggling after power-up and be continuous while power is applied. XTAL When using an oscillator output instead of a crystal, the XTAL output signal should not have a capacitor to ground. It is shown this way on some EZ-KIT Lite board schematics. Note that it is not populated on the board, and it should not be populated in an end design. Crystal Inputs In addition to the clock source for the processor core CCLK (Core Clock) and the peripheral clock SCLK (System Clock), some Blackfin processors have additional clock domains. Examples are Real-Time Clock, Ethernet, USB (Universal Serial Bus) and MXVR. Like CLKIN and XTAL, these clock domains can use a crystal or an external clock can drive the input signal. The external clock may be square wave or sinusoidal. If using a sine wave, the voltage levels must be kept within the minimum and maximum limits found in the datasheet. Some peripheral XTAL pins may also be driven by the CLKBUF output of some processors. If using an external clock instead of a crystal, the corresponding XTAL output signal must be left floating. If using a crystal, check the datasheet and crystal specifications for recommended series or parallel resistors. It is important not to overdrive small crystals. If a clock domain is not used by your application, pull the input clock high or low to prevent oscillation. Power Regulator A software controlled internal regulator circuit using an external FET, diode and inductor is offered on some Blackfin family processors. The core voltage (VDDINT) can also be powered with standard external regulation. The internal voltage regulator may be an attractive option for some designs using power management that controls both clock speed and core voltage. Be aware that the internal voltage regulator is a switching regulator circuit (not a linear regulation circuit). Ensure that the diode shown in the data sheet is present. Keep the VROUT signal trace short, as this signal can be a source of radiated noise! Refer to the application note Switching Regulator Design Considerations for ADSP (Analog Digital Signal Processor)-BF533 Blackfin Processors (EE-228)[3] for further details on component selection. New power control functions have been added to some Blackfin Processors. A VRSEL input selects internal regulator or external regulator mode. An EXT_WAKE output may be provided to turn off an external regulator when using hibernate state. It is a high true power-up signal that can be connected directly to the low true shut down input of many regulators. A PG or SS/PG signal is a feature on some processors. In internal mode, SS/PG can be used to give a Soft Start at power up and at the end of hibernate. In external mode, it can be used as a low true Power-Good signal to safely start core processing after wake from hibernate mode. Multiple Power Domains Does your design require a battery for continuous time information? If not, connect the RTC (Real Time Clock) power to VDDEXT even if the RTC (Real Time Clock) is not used. All power and ground signals must be connected at levels described in the datasheet. This is true if you do not use the associated peripheral and is even true if the peripheral does not exist on the processor being used in the design. Failure to drive all voltage connections may result in JTAG (Joint Test Action Group - low level interface to cpu) failures and improper initialization and operation. USB OTG Interface Several members of the Blackfin family of processors allow a direct physical USB (Universal Serial Bus) interface. This is also called the Universal Transceiver Macro Interface in the hardware reference manuals. USB Clocking of USB_XI An external crystal or crystal oscillator is required to generate the internal USB2 high-speed clock. The frequency should be chosen to operate the internal clock at 960 MHz (Megahertz). External frequency and programmed multiplication values can be any combination that gives a half speed clock of 480 MHz (Megahertz). The circuit shown in the corresponding datasheet for CLKIN connections can also be used as an example for this clock. USB_ID USB (Universal Serial Bus)_ID is unique to USB (Universal Serial Bus) OTG. It allows the OTG cable to determine host (A-Device) or peripheral (B-Device) initial status of the interface. If not using OTG but using the USB (Universal Serial Bus) interface as a host (A-Device), this pin should be grounded. If not using OTG but using the interface as a USB (Universal Serial Bus) peripheral (B-Device), USB (Universal Serial Bus)_ID can be left floating or connected to a weak pull-up. D+ and D- Connection The Blackfin USB (Universal Serial Bus)_DP and USB (Universal Serial Bus)_DM signals should be routed as an impedance-controlled differential pair directly to the D+ and D- of the USB (Universal Serial Bus) connector. Traces should have no extraneous side traces, sometimes called stubs. Further care should be taken to isolate this differential pair from high-speed signals or other noise sources like VROUT. The Blackfin processor provides termination resistance needed for OTG compliance. USB_VBUS Connection USB (Universal Serial Bus)_VBUS is an input to the processor, except when programmed to output Session Request pulses. When using host or OTG (A-Device) mode, an external 5 V source of more than 8 mA is required to drive USB (Universal Serial Bus)_VBUS on the cable. This supply needs to be fully disabled when in OTG (B-Device) mode. A GPIO (General Purpose Input/Output) signal should be used for enable/disable. USB (Universal Serial Bus)_VBUS should be connected directly to the USB (Universal Serial Bus) connector. Check the datasheet for 5 V tolerance of USB (Universal Serial Bus)_VBUS. Some processors are not 5 V-tolerant if VDDUSB external power is zero volts. A few applications may expect their products to experience very long exposure to 5 V on USB (Universal Serial Bus)_VBUS when the processor has no local power. These applications may wish to provide power to VDDUSB by using the 5 V power from USB (Universal Serial Bus)_VBUS. An example of such a protection circuit can be found in the ADSP (Analog Digital Signal Processor)-BF548 EZ-Kit lite schematics. USB (Universal Serial Bus) ESD (electrostatic discharge) Protection Additional ESD (electrostatic discharge) protection is recommended on cable signals USB (Universal Serial Bus)_DP, USB (Universal Serial Bus)_DM, USB (Universal Serial Bus)_ID, and USB (Universal Serial Bus)_VBUS. Protection devices should be placed near the connector.