34
MAX3421E Programming Guide
GPXB, GPXA
Meaning:
Two bits, GPXB and GPXA, determine the output of the GPX pin.
Mode: Peripheral
and
Host
The CPU sets and clears these bits.
Programming Notes
The GPX pin can output one of four internal signals, as shown in the table below:
GPXB GPXA GPX Pin
0
0
OPERATE (complement of internal POR)
0 1
VBUS
Detect
1
0
BUSACT or INIRQ*
1
1
SOF (0-1 transition when SOF packet
arrives, 50% duty-cycle signal)
*
If SEPIRQ = 1
The default setting for the GPX output when GPXB = 1 and GPXA = 0 is BUSACT. However, if
the SEPIRQ bit is set to 1, the BUSACT signal is replaced by an interrupt request signal that is
active whenever one of the eight GPIN pins makes a 0-1 or 1-0 transition. In this case the GPX
pin serves as a second interrupt pin (along with INT), with the same configuration (level or edge,
edge polarity) as the INT pin. See page
for more information about the SEPIRQ bit.