Altera Embedded Peripherals IP Instrukcja Użytkownika Strona 116

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As an example, assume that the SPI core is idle (that is, the txdata register and transmit shift register are
empty), when a CPU writes a data value into the txdata holding register. The TRDY bit is set to 0
momentarily, but after the data in txdata is transferred into the transmitter shift register, TRDY returns to
1. The CPU writes a second data value into the txdata register, and again the TRDY bit is set to 0. This
time the shift register is still busy transferring the original data value, so the TRDY bit remains at 0 until the
shift operation completes. When the operation completes, the second data value is transferred into the
transmitter shift register and the TRDY bit is again set to 1.
status Register
The status register consists of bits that indicate status conditions in the SPI core. Each bit is associated
with a corresponding interrupt-enable bit in the control register, as discussed in the Control Register
section. A master peripheral can read status at any time without changing the value of any bits. Writing
status does clear the ROE, TOE and E bits.
Table 10-6: status Register Bits
# Name Description
3 ROE Receive-overrun error
The ROE bit is set to 1 if new data is received while the rxdata register is full (that is,
while the RRDY bit is 1). In this case, the new data overwrites the old. Writing to the
status register clears the ROE bit to 0.
4 TOE Transmitter-overrun error
The TOE bit is set to 1 if new data is written to the txdata register while it is still full
(that is, while the TRDY bit is 0). In this case, the new data is ignored. Writing to the
status register clears the TOE bit to 0.
5 TMT Transmitter shift-register empty
In master mode, the TMT bit is set to 0 when a transaction is in progress and set to 1
when the shift register is empty.
In slave mode, the TMT bit is set to 0 when the slave is selected (SS_n is low) or when
the SPI Slave register interface is not ready to receive data.
6 TRDY Transmitter ready
The TRDY bit is set to 1 when the txdata register is empty.
7 RRDY Receiver ready
The RRDY bit is set to 1 when the rxdata register is full.
8 E Error
The E bit is the logical OR of the TOE and ROE bits. This is a convenience for the
programmer to detect error conditions. Writing to the status register clears the E bit
to 0.
control Register
The control register consists of data bits to control the SPI core's operation. A master peripheral can read
control at any time without changing the value of any bits.
10-10
status Register
UG-01085
2014.24.07
Altera Corporation
SPI Core
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