Address Selection Rotary Switches
For flexibility with most SW and Development libraries this unit will support any valid address
between 0x000-0x007 and 0x7F8-0x7FF. However, most platforms have limited IO space.
Please refer to your host CPU IO Map for available IO space for this product.
Most applications will use one of the common serial port addresses. The most common are:
COM1 = 3F8, IRQ4, COM2 = 2F8, IRQ3 COM3 = 3E8, IRQ4 COM4 = 2E8, IRQ3. Figure 1 shoes
0x3f8 for the GPS Data Port, 0x2f8 for the GPS Differential Port and 0x300 for the External
Serial Port.
This unit is simple to use. Set the selected channel address switches to the IO space you want
and the channel is ready to use.
Please note, when selecting the LSB of each serial port only bit 3 is changed. Thus a setting
of 0 or 8 is valid. Any selection between 0 and 7 (BIT 3 = 0) and 8 and 15 (BIT 3 = 1) has no
effect other than to set BIT 3. Confused? This means BIT’s 0-2 are masked and have no ef-
fect on the base address. ISA IO blocks are assigned in 8 byte blocks. Thus a base address
of 0x3f0 or 0x3f8 makes sense. However, a base address of 0x3f9 does not. Address bits
0-2 are routed directly to the UARTS and are not used in base IO address decoding. Only
bits 3 to 15 are used for address decoding.
So if you set the rotary switches to an IO space of 0x3f9 the device still maps to a base IO of
0x3f8.
Internal or Auxiliary 1 Pulse Per Second (1PPS) Selection, JP1
JP1 Controls the 1PPS source and HW or SW control of the source.
In position SW the 1PPS signal is routed based upon the level of the RTS line of the Data Port.
Thus if the data port is COM1 (0x3F8) then setting the RTS bit of COM1 to 1 will select the AUX
PPS input and setting the RTS bit to 0 will select the GPS.
In position JP the data, PPS signal and Reset lines are routed based upon Jumper JP1, not the
RTS bit of the Data Port. JP1A GPS selects the Novatel SSII for the 1PPS source and JP1A AUX
selects the AUX for the 1PPS source.
PPS Output Signal Inversion, JP2 & JP3
There are two PPS Outputs available. One is RS-232 level and the other is TTL Level. JP2 and
JP3 control the inversion of the respective PPS outputs as well as allow either jumper settings
or software control of the inverters.
JP2 controls the RS-232 level inversion exclusively. The SW position allows inversion to be set
by the RTS1 BIT of the Differential Port. The JP position selects jumper control. N = Normal
or Un-Inverted, I = Inverted.
JP3 controls the TTL level inversion exclusively. The SW position allows inversion to be set by
the RTS1 BIT of the Differential Port. The JP position selects jumper control. N = Normal or
preliminary
6
REV B
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