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1990-11-05
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APPENDIX Q -- RBBS-PC and the IBM PCjr Q-1
APPENDIX Q -- RBBS-PC and the IBM PCjr
--------------------------------------
RBBS-PC adheres to the Hayes standards for autoanswer applications that are
described in Section 9, "Writing Programs for the Smartmodem 1200," of the
SMARTMODEM 1200 HARDWARE REFERENCE MANUAL. Under the section entitled
"Additional Program Considerations" Hayes recommends that autoanswer
applications (like RBBS-PC) "... force the modem to answer the call (ATA)
rather than allowing the modem to automatically answer...." Beginning
with 13.1A, RBBS-PC no longer REQUIRES the Ring Indicator signal from the
modem (pin 22) in order to answer the phone (except if parameter 224 of
CONFIG is non-zero).
Here are some facts about the PCjr:
1) The PCjr's external modem interface does not have a Ring Indicator
signal.
2) The PCjr requires that an external modem be opened as COM1 if no
internal modem is installed. However, if no internal modem exists the
PCjr requires that the COM2 RS-232 registers be used even though the
port has been opened as COM1. Technically this is described as using
the external RS-232 asynchronous adapter as logical channel 1 (i.e.
COM1) but manipulating it as physical channel 2 (i.e. COM2). This
occurs on a PCjr only when an internal modem is NOT present and the
external RS-232 interface is.
3) The 128K PCjr only provides 90K of usable RAM (the rest is used by
DOS, the monitor's buffers, etc.). Fortunately PCjr owners can get up
to 512K of RAM with "add-on" equipment (from IBM and others) in order
to have enough RAM for RBBS-PC to run in.
4) The standard PCjr supplied by IBM does not have a DMA and hence can't
do communications I/O simultaneously while doing disk I/O.
RBBS-PC beginning with version 13.1A will run an IBM PCjr providing that
the PCjr
1) Has at least 320K of memory.
2) Disk I/O does not occur simultaneously with communications I/O (i.e.
either you have a second disk drive with a DMA or you set BUFFERS=0).
3) One of the following three modem configurations are used:
- An internal PCjr modem with an external Hayes modem where the external
Hayes modem is used for RBBS-PC.
- No internal PCjr modem with an external Hayes modem used for RBBS-PC.
- Only an internal PCjr modem and it is used for RBBS-PC.
The following discusses each of these three modem configurations supported
by RBBS-PC with the PCjr.
Internal PCjr Modem with RBBS-PC Using External Hayes Modem
-----------------------------------------------------------
This configuration means that the PCjr has both a COM1 (the internal PCjr
modem) and a COM2 (the external Hayes modem). RBBS-PC is set up to use
COM2. No changes are required to for RBBS-PC for this type of PCjr
configuration. CONFIG parameter 224 should be set to 0. This will cause
RBBS-PC to set the external Hayes modem into "auto-answer" mode and RBBS-PC
will wait for carrier detect. This is the way that RBBS-PC overcomes the
PCjr's lack of "ring-indicator" signal for the external communications
port.
RBBS-PC 17.3A TECHNICAL REFERENCE MANUAL Q-2
No Internal PCjr Modem With RBBS-PC Using External Hayes Modem
--------------------------------------------------------------
This configuration means that the PCjr has only one RS-232 interface -- the
external Hayes modem. This must be opened as COM1 but use COM2's registers
to control the communications port (believe it or not that's the way IBM
designed the PCjr).
CONFIG parameter 221 should be used to indicate that COM1 is being used.
Unfortunately the current BASIC compilers (both IBM's Version 2 and
Microsoft's QuickBASIC) are incapable of handling a communication port as
logical device 1 (i.e. COM1) but on physical channel 2 (i.e. the interrupts
are for COM2).
Should this ever be fixed by either IBM or Microsoft, CONFIG parameter 29
should be used to indicate that no internal PCjr modem is installed. This
tells CONFIG to make sure that COM2 registers are used to manipulate the
PCjr's external communications port.
Until this is fixed by the respective vendors, the PCjr user will have to
run a utility like COMSWAP that exchanges the pointers between COM1 and
COM2 within DOS.
In either case, CONFIG parameter 224 should be set to 0. This will cause
RBBS-PC to set the external Hayes modem into "auto-answer" mode and RBBS-PC
will wait for carrier detect. This is the way that RBBS-PC overcomes the
PCjr's lack of "ring-indicator" signal for the external communications
port. Again no changes to RBBS-PC are required for this type of PCjr
configuration.
Only An Internal PCjr Modem for RBBS-PC and NO External Hayes Modem
-------------------------------------------------------------------
For this type of PCjr configuration, you can take the CONFIG default
settings for the communications port (COM1) and specify that you are
running on a PCjr (parameter 29). However, make sure that CONFIG parameter
228 specifies that the modem is to be opened at 300 baud. Of course, RBBS-
PC will be only able to answer the telephone at 300 baud and send and
receive data from users who log on with their communications parameters set
at N/8/1 (i.e. no parity, eight data bits, and one stop bit) since RBBS-PC
is limited by the PCjr's own modem's limitations.
RBBS-PC already has the modem commands for the PCjr's very strange internal
modem in the logic to answer the phone so no changes to the .DEF file are
required.