IDT Serial Peripheral Interface
Block Diagram
79RC32438 User Reference Manual
16 - 2
November 4, 2002
Notes
When the PCI interface completes reading configuration information from the PCI serial EEPROM, it tri-
states the SCK and SDO pins and drives PCIGNTN[1] low (i.e., it negates the chip select). This allows the
SCK, SDO, and SDI pins to be used by the SPI Interface.
After a reset, the SPI interface is initially disabled. When the PCI interface completes reading configura-
tion information from the PCI serial EEPROM, the SPI interface may be enabled by setting the SPE bit in
the SPI control register. The SPI interface may not be enabled before the PCI serial EEPROM has
completed reading configuration information (i.e., before the PCI Serial EEPROM Done (EED) bit is set in
the PCIS register). Attempting to enable the SPI interface while the interface is in use by the PCI interface
does not damage the RC32438 (i.e., no dual sourcing), but it does produce unpredictable results. When the
PCI mode is not PCI satellite mode with suspended CPU execution, the SPI interface may be enabled at
any time since the PCI interface will not read the PCI serial EEPROM.
When the SPI interface is enabled, it drives the SC and SDO pins. When an SPI transaction is initiated
by writing to the SPI Data Register (SPD), the SCK, SDO, and SDI signals are used to transfer data. A
general purpose I/O pin must be used as the SPI chip select, and this pin must be managed by software.
In systems where multiple SPI devices are required, multiple general purpose I/O pins may be used as
SPI chip selects. In these scenarios, the GPIO pins used as chip selects must be managed by software.
In cases where the SPI interface is not enabled, the serial I/O pins are not used as bit I/O ports and the
SCK, SDO, and SDI pins are tri-stated after the loading of configuration information is complete. Pull-ups or
pull-downs are necessary on the board. (Refer to the second to the last row in Table 16.1.)
When the SPIE bit is set in the SPC register, the SPI interrupts are enabled. An SPI interrupt is gener-
ated when the MODF or SPIF bits are set in the SPS register.
P
P
L
1
1.
PCI Serial EEPROM loading only occurs in PCI satellite mode with suspended execution. In PCI satellite mode with PCI
target not ready, the PCI serial EEPROM loading is effectively always completed.
2.
Don’t care
3.
Tri-stated
4.
State determined by PCI function in corresponding PCI mode
5.
Output
6.
Input
7.
This signal is driven low (MICROWIRE chip select is negated).
S
E
C
S
(
C
S
Serial I/O Pins
S
S
S
P
No
X
2
No
0
X
Z
3
Z
Z
O
4
No
X
Yes
0
Z
O
5
O
I
6
O
4
No
X
X
1
0
I
I
I
O
4
Yes
Yes
X
1
0
I
I
I
I
No
X
X
1
1
O
O
O
O
4
Yes
Yes
X
1
1
O
O
O
O
Yes
No
X
X
X
O
O
I
O
Yes
Yes
No
0
X
Z
Z
Z
O
7
Yes
Yes
Yes
0
X
O
O
I
O
7
Table 16.1 Serial I/O Pin Configuration