Texas Instruments MSC1210 manual 13-12

Models: MSC1210

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SPI Master Transfer in FIFO Mode using Interrupts

Line 11 enables the SPIRX and SPITX interrupts, after which the AI flag is cleared and the EAI flag is enabled. There is no data to transmit, so SPITXIRQ goes up and we go to the monitor_isr() routine. The SPITX IRQ went up, so the subroutine send_4_bytes is called, where the program writes to the SPIDATA register 4 times.

In line 20, the AI flag is cleared. The interrupt SPITX goes on again immediate- ly because the interrupt is configured to be triggered when the number of bytes to transmit is 4 or fewer. The number to bytes to transmit are 4, so the interrupt is triggered and 4 additional bytes are subsequently written to the buffer.

Thus, the buffer is completely filled with bytes to be transmitted. As one byte is transmitted, an additional byte is written. Once 4 bytes are transmitted, 4 by- tes will be received, at which point both transmit and receive interrupts go high. At that point the interrupt routine is executed, first reading the 4 received bytes and then writing 4 more bytes to be transmitted. In this manner, the buffer is always used to its fullest extent without overflowing in either direction.

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Page 174
Image 174
Texas Instruments MSC1210 manual 13-12