JANUS? 2020 Hand-Held Computer (4MB) - Intermec

JANUS 2020 Hand-Held Computer User’s Manual (4MB) NF BC
6-8
Understanding How IRQs Affect COM Ports
According to the industry standard architecture (ISA) for PCs, the COM ports
on a PC must share hardware interrupt requests (IRQs). Because your JANUS
reader is PC compatible, the reader’s COM ports also share IRQs:
IRQ3 is assigned to both COM2 and COM4.
IRQ4 is assigned to both COM1 and COM3.
The ISA practice of sharing IRQs causes limitations on the JANUS readers:
• The Intermec protocol handlers, PHIMEC and PHPCSTD, cannot share
IRQs. You can load PHIMEC or PHPCSTD only on COM1.
• The Intermec RF protocol handler (RFPH) uses “logical COM ports.” RFPH
designates the RF port as “logical COM4” but does not use IRQ3. Instead,
IRL uses the logical port numbers to direct transmits and receives. For
example, X4P transmits using “logical COM4.”
• Intermec recommends that you do not designate any JANUS port as
COM3. Because COM1 and COM3 share an IRQ, you cannot use COM1 if
you use COM3.