Datasheet
MAX3421E
USB Peripheral/Host Controller
with SPI Interface
18
Maxim Integrated
GPOUT7–GPOUT0
The SPI master controls the GPOUT3–GPOUT0 states
by writing to bit 3 through bit 0 of the IOPINS1 (R20)
register. GPOUT7–GPOUT4 states are controlled by
writing to bit 3 through bit 0 of the IOPINS2 (R21) regis-
ter. GPOUT7–GPOUT0 logic levels are referenced to
the voltage on V
L
. As shown in Figure 13, reading the
state of a GPOUT7–GPOUT0 bit returns the state of the
internal register bit, not the actual pin state. This is use-
ful for doing read-modify-write operations to an output
pin (such as blinking an LED), since the load on the
output pin does not affect the register logic state.
GPX
GPX is a push-pull output with a 4-way multiplexer that
selects its output signal. The logic level on GPX is refer-
enced to V
L
. The SPI master writes to the GPXB and
GPXA bits of PINCTL (R17) register to select one of five
internal signals as depicted in Table 5.
• OPERATE: This signal goes high when the
MAX3421E is able to operate after a power-up or
RES reset. OPERATE is active when the RES input
is high and the internal power-on-reset (POR) is
not asserted. OPERATE is the default GPX output.
• VBUS_DET: VBUS_DET is the VBCOMP comparator
output. This allows the user to directly monitor the
V
BUS
status.
• BUSACT: USB BUS activity signal (active high).
This signal is active whenever there is traffic on
the USB bus. The BUSACT signal is set whenever
a SYNC field is detected. BUSACT goes low during
bus reset or after 32-bit times of J-state.
REGISTER BIT
GPOUT
WRITE
GPOUT
READ
GPOUT
PIN
Figure 13. Behavior of Read and Write Operations on
GPOUT3–GPOUT0
FULL-SPEED
TIME FRAME
1ms
FULL-SPEED
TIME FRAME
1ms
SOF
USB
PACKETS
GPX
SOF SOF
~50%
Figure 14. GPX Output in SOF Mode
SPI
CONTROLLER
SPI
CONTROLLER
MAX3421E
MAX3421E
MOSI
MISO
MOSI
MISO
FDUPSPI = 0 (DEFAULT)
FDUPSPI = 1
Figure 15. MAX3421E SPI Data Pins for Full-Duplex (Top) and
Half-Duplex (Bottom) Operation
Table 5. GPX Output State Due to GPXB
and GPXA Bits
GPXB GPXA GPX PIN OUTPUT
0 0 OPERATE (Default State)
0 1 VBUS_DET
1 0 BUSACT/INIRQ*
1 1 SOF
*
If SEPIRQ = 1.