The serial port reset functionality of the VS1053 Simple DSP Host board has raised some questions. The DTR line of the serial port can be used with the host board to reset the VS1053. The polarity of the DTR line is nonstandard, but there is a good reason for it.
A PC application can set the state of the DTR signal on the RS-232 port as it wishes. Terminal programs set the state of the DTR to be "READY" when they are active. Otherwise the state of the DTR pin is "NOT READY". The VS1053 Simple DSP Host Board resets the VS1053 when the DTR is in "READY" state. This might first seem to be a weird selection, but it's actually quite clever. Our connection allows the DSP to be running even when there is no RS-232 cable attached, or there is no RS-232 program running in the PC. The Windows version of VSIDE keeps the DTR pin in the "NOT READY" state to allow the DSP to remain running. The VS1053 can be programmatically resetted by running an external helper application which toggles the DTR signal.
Problems arise when you try to use the RS-232 port of the Host board to communicate with the VS1053 with a terminal program such as HyperTerminal. The terminal program asserts DTR to "READY" which in effect halts the VS1053. The solution is to remove resistor R2 from the Host board. It is located next to the "RS" pin of the pin header connector.
VS1053 Simple DSP host board:
Designing hardware that use VLSI Solution's devices as the system controller for the entire design.
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