
B-1
8586A—RFID—5/09
Appendix B
The SPI Serial Interface
The SPI Interface mode is selected by shorting the ISEL pin to Vcc. Six microcontroller pins are
required to operate AT88RF1354 in SPI mode. The ISTAT signal is used for handshaking
between the microcontroller and RF reader.
B.1
SPI Interface
The AT88RF1354 SPI interface operates as a slave device in SPI mode 0. In SPI mode 0 the
polarity and phase of the serial clock in relation to the data is as follows:
SCK is low when IDLE.
Incoming data on SDI is sampled on the positive edge of SCK.
Outgoing data on SDO is setup on the negative edge of SCK. (The host microcontroller samples
SDO on the positive edge of SCK)
ISTAT reports the serial interface status to the microcontroller.
Figure 7.
Serial Interface Wiring to SPI Microcontroller
R e a d e r IC
A T 8 8 R F 1 3 5 4
(S P I S la ve )
M ic ro c o n tro lle r
(S P I M a ste r)
R e se tB
IS E L
S C K
S D I
S D O
S S B
Istat
o u tp u t
V C C
in p u t
S C K
M O S I
M IS O
S S B
A high level on the ISTAT pin signals the host microcontroller that a byte of data is ready to be
read from the AT88RF1354 serial interface. If another byte is immediately available on the serial
port, ISTAT will go low for 150 uS, then return high. ISTAT will remain high until the last bit of the
byte is read, when it will return low. All data must be clocked out of the AT88RF1354 before it
can receive a command.