
Philips Semiconductors
Synchronous Serial Interface
PRODUCT SPECIFICATION
17-7
17.7
INTERRUPT GENERATION
Depending on the settings of the TIE, RIE and CDE bits
in the SSI_CTL register, the SSI unit can generate inter-
rupts. This is best illustrated by Figure 17-8. Note:
RXFES and TXFES are the internal receive and transmit
framing error conditions. When an SSI interrupt is detect-
ed, the interrupt service routine should check all status
bits.The interrupts should be set up as level-triggered in-
terrupts.
17.8
16-BIT ENDIAN-NESS AND SHIFT
DIRECTION
The SSI unit supports both access orders for the 16-bit
halves of a machine word. In addition, the shift direction
can be controlled to select MSB or LSB shifting first. The
SSI_CTL.EMS bit controls the 16-bit endian mode, and
the TSD and RSD bits control transmit and receive shift
direction.
When EMS is set, the rst data word received in a frame
will be transferred to bit 15-0 of the SSI_RxDR, the sec-
ond word will be transferred to bits 31-16 of the
SSI_RxDR. EMS = ‘0’ reverses the order of the halves of
SSI_RxDR. Likewise in the transmitter, when EMS is set,
the rst data word transmitted in a frame will be bits 15-
0 of SSI_TxDR, the second word transferred will be bits
31-16 of SSI_TxDR.
TSD and RSD control the shift direction of transmit and
receive shift registers (TxSR and RxSR). Transmit data is
transmitted MSB rst when TSD is ‘0’ or LSB rst other-
wise. Receive data is received MSB rst when RSD
equals ‘0’, LSB rst otherwise.
For
an
example
of
the
transmit
operation
see
Figure 17-9. Receive works the same, only that data is
shifted in
.
Figure 17-8. Interrupt generation logic.
TUE
and
or
TDE
TXFES
TIE
ROE
and
or
RDF
RIE
or
SSI interrupt
CDE & CDS
RXFES
Figure 17-9. 16-bit endian and shift direction operation.
SSI_TXDR
31
0
15
SSI_RXFSX
SSI_TXDATA
D16 D15 D14 D13 ....... D2
D1
D0
D31 D30 D29 ....... D18 D17 D16 D15 D14 D13 ......
1st word
3th word
SSI_RXFSX
SSI_TXDATA
D31 D0
D1
D2
....... D13 D14 D15 D16 D17 D18 ....... D29 D30 D31 D0
D1
D2
......
1st word
3th word
SSI_RXFSX
SSI_TXDATA
D0
D31 D30 D29 ....... D18 D17 D16 D15 D14 D13 ....... D2
D1
D0
D31 D30 D29 ......
1st word
3th word
SSI_RXFSX
SSI_TXDATA
D15 D16 D17 D18 ....... D29 D30 D31 D0
D1
D2
....... D13 D14 D15 D16 D17 D18 ......
1st word
3th word
2nd word
EMS = 1, TSD = 0
EMS = 1, TSD = 1
EMS = 0, TSD = 0
EMS = 0, TSD = 1