Interfaces and Connectors
VL-EPICs-36 Reference Manual
44
SPISTATUS (READ/WRITE) CA9h (or C99h)
D7
D6
D5
D4
D3
D2
D1
D0
IRQSEL1
IRQSEL0
SPICLK1
SPICLK0
HW_IRQ_EN LSBIT_1ST
HW_INT
BUSY
Table 22: SPI Control Register 2 Bit assignments
Bit
Mnemonic
Description
D7-D6
IRQSEL
IRQ Select
– These bits select which IRQ will be asserted when a
hardware interrupt from a connected SPI device occurs. The
HW_IRQ_EN bit must be set to enable SPI IRQ functionality.
IRQSEL1 IRQSEL0 IRQ
0
0
IRQ3
0
1
IRQ4
1
0
IRQ5
1
1
IRQ10
Note:
The on-board digital I/O chips must be configured for open-drain
and mirrored interrupts in order for any SPI device to use hardware
interrupts.
D5-D4
SPICLK
SPI SCLK Frequency –
These bits set the SPI clock frequency.
SPICLK1 SPICLK0 Frequency
0
0
1.042 MHz
0
1
2.083 MHz
1
0
4.167 MHz
1
1
8.333 MHz
D3
HW_IRQ_EN
Hardware IRQ Enable
– Enables or disables the use of the selected
IRQ (IRQSEL) by an SPI device.
0 = SPI IRQ disabled, default
1 = SPI IRQ enabled
Note:
The selected IRQ is shared with PC/104 ISA bus devices. CMOS
settings must be configured for the desired ISA IRQ.
D2
LSBIT_1ST
SPI Shift Direction
– Controls the SPI shift direction of the SPIDATA
registers. The direction can be shifted toward the least significant bit or
the most significant bit.
0 = SPIDATA data is left-shifted (MSbit first), default
1 = SPIDATA data is right-shifted (LSbit first)
D1
HW_INT
SPI Device Interrupt State –
This bit is a status flag that indicates
when the hardware SPX signal SINT# is asserted.
0 = Hardware interrupt on SINT# is deasserted
1 = Interrupt is present on SINT#
This bit is read-only and is cleared when the SPI device’s interrupt is
cleared.
D0
BUSY
SPI Busy Flag
– This bit is a status flag that indicates when an SPI
transaction is underway.
0 = SPI bus idle
1 = SCLK is clocking data in and out of the SPIDATA registers
This bit is read-only.
