
Most bits (IROE, ITOE, ITRDY, IRRDY, and IE) in the control register control interrupts for status
conditions represented in the status register. For example, bit 1 of status is ROE (receiver-overrun
error), and bit 1 of control is IROE, which enables interrupts for the ROE condition. The SPI core asserts an
interrupt request when the corresponding bits in status and control are both 1.
Table 10-7: control Register Bits
# Name Description
3 IROE Setting IROE to 1 enables interrupts for receive-overrun errors.
4 ITOE Setting ITOE to 1 enables interrupts for transmitter-overrun errors.
6 ITRDY Setting ITRDY to 1 enables interrupts for the transmitter ready condition.
7 IRRDY Setting IRRDY to 1 enables interrupts for the receiver ready condition.
8 IE Setting IE to 1 enables interrupts for any error condition.
10 SSO Setting SSO to 1 forces the SPI core to drive its ss_n outputs, regardless of whether
a serial shift operation is in progress or not. The slaveselect register controls which
ss_n outputs are asserted. SSO can be used to transmit or receive data of arbitrary
size, for example, greater than 32 bits.
After reset, all bits of the control register are set to 0. All interrupts are disabled and no ss_n signals are
asserted.
slaveselect Register
The slaveselect register is a bit mask for the ss_n signals driven by an SPI master. During a serial shift
operation, the SPI master selects only the slave device(s) specified in the slaveselect register.
The slaveselect register is only present when the SPI core is configured in master mode. There is one
bit in slaveselect for each ss_n output, as specified by the designer at system generation time.
A master peripheral can set multiple bits of slaveselect simultaneously, causing the SPI master to
simultaneously select multiple slave devices as it performs a transaction. For example, to enable
communication with slave devices 1, 5, and 6, set bits 1, 5, and 6 of slaveselect. However, consideration
is necessary to avoid signal contention between multiple slaves on their miso outputs.
Upon reset, bit 0 is set to 1, and all other bits are cleared to 0. Thus, after a device reset, slave device 0 is
automatically selected.
Document Revision History
Table 10-8: Document Revision History
Date and
Document
Version
Changes Made Summary of Changes
December
2010
v10.1.0
Removed the “Device Support”, “Instantiating the
Core in SOPC Builder”, and “Referenced
Documents” sections.
—
UG-01085
2014.24.07
slaveselect Register
10-11
SPI Core
Altera Corporation
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