Some considerations for DSP hardware design

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Some considerations for DSP hardware design [Copy link]

Principles for selecting clock circuits
1. When multiple clock signals of different frequencies are required in the system, programmable clock chips are preferred;
2. When a single clock signal is used, a crystal clock circuit is selected;
3. When multiple clock signals of the same frequency are used, a crystal oscillator is selected;
4. Try to use the PLL inside the DSP chip to reduce the frequency of the external clock and improve the stability of the system;
5. DSP chips such as C6000, C5510, C5409A, C5416, C5420, C5421 and C5441 do not have an oscillation circuit inside, so crystal clock circuits cannot be used;
6. The clock signal level of DSPs such as VC5401, VC5402, VC5409 and F281x is 1.8V. It is recommended to use a crystal clock circuit.
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Handling of unused input/output pins
1. Unused input pins cannot be left floating, but should be pulled up or down to a fixed level
1) Key control input pins, such as Ready, Hold, etc., should be fixed to the appropriate state. The Ready pin should be fixed to the valid state, and the Hold pin should be fixed to the invalid state
2) No connection (NC) and reserved (RSV) pins, NC Pins: Unless otherwise specified, these pins are left unconnected. RSV pin: Whether to connect or not should be determined according to the data sheet.
3) Non-critical input pins, pull them up or down to a fixed level to reduce power consumption.
2. Unused output pins can be left unconnected.
3. Unused I/O pins: If the default state is an input pin, treat them as non-critical input pins and pull them up or down to a fixed level; if the default state is an output pin, they can be left unconnected.
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Why is the DSP with large on-chip RAM more efficient?
　 At present, the on-chip RAM of DSP is getting larger and larger. To design an efficient DSP system, you should choose a DSP with large on-chip RAM. Compared with off-chip memory, on-chip RAM has the following advantages: 1) The on-chip RAM is faster, which can ensure that the DSP runs without waiting. 2) For the C2000/C3x/C5000 series, some on-chip memories can be accessed twice in one instruction cycle, making the instructions more efficient. 3) The on-chip RAM runs stably and is not affected by external interference, nor will it interfere with the outside. 4) The DSP has multiple buses on the chip. When accessing the on-chip RAM, it will not affect the access of other buses, and the efficiency is high.
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How to program the external Flash
of DSP? DSP external Flash programming method:
1. Programming through the programmer: Convert the OUT file to a format acceptable to the programmer through the HEX conversion program, and then program it through the programmer.
2. Programming through DSP software: You need to program the Flash programming program according to the Flash instructions, load the application program and the Flash programming program into RAM respectively, and run the programming program to program.
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DSP external memory control method
For general memory, there are control signals such as RD, WR and CS. Many DSPs (C3x, C5000) do not have control signals to directly connect to the memory. The general method is as follows:
1. CS is generated by address line and PS, DS or STRB decoding; 2. /RD= /STRB+/R/W
; 3. /WR=/STRB+R/W.
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How to mix 5V/3.3V?
The development of TI DSP is similar to the development of integrated circuits. New DSPs are all 3.3V, but many peripheral circuits are still 5V. Therefore, in DSP systems, there are often problems with 5V and 3.3V DSPs being mixed. In these systems, it should be noted that: 1) DSP outputs to 5V circuits (such as D/A) without adding any buffer circuits and can be directly connected. 2) DSP inputs 5V signals (such as A/D). Since the voltage of the input signal is >4V, it exceeds the power supply voltage of the DSP. The external signal of the DSP has no protection circuit and needs to be buffered, such as 74LVC245, to convert the 5V signal into a 3.3V signal. 3) The signal of the emulator's JTAG port must also be 3.3V, otherwise the DSP may be damaged.
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Basic conditions for DSP operation:
1) The DSP power supply and ground are connected correctly.
2) The DSP clock is correct.
3) The DSP control signal RS and HOLD signal are connected to a high level.
4) Turn off the watchdog of C2000.
5) Pull up the non-maskable interrupt NMI
6) Pull up the READY pin