Advanced Communication Board Developer Toolkit 

ABSTRACT:  DMA3.C

DMA3.C is an Direct Memory Access BISYNC loop-back program. The base
address is 238 Hex and no IRQ is used for this test. DMA jumpers on the ACB
card should be set for WAIT/REQ on receive for DMA channel 1 and DTR/REQ on
transmit for DMA channel 3.  The "DMA always enabled" jumper on the ACB must
be "ON". No additional jumpers are needed. To build the program, the
ACB.OBJ and the DMA.OBJ file must be linked from the \LIBRARY directory.

This program is set up for BISYNC at 19.2K bps. This program will transmit
and receive all characters as a BISYNC message using DMA. The program will
terminate when the DMA channel 1 has reached Terminal Count or any key on the
keyboard is pressed. Keep in mind that this example is a very simple DMA
program. A combination of DMA and interrupts yields the highest throughput
on an ACB adapter.

Please note that this example uses full duplex DMA. The ACB-II only supports
half duplex DMA. Either the program or your ACB-II should be modified to use
this program. Please refer to the \APP_NOTE directory on this diskette for
details on ACB-II full duplex modifications.

Cables:

For BISYNC mode, transmit, receive, Tx Clock, and Rx Clock are needed. The
program may be used in a stand alone loop-back configuration, or with another
PC with an ACB or BISYNC adapter installed. For most ACB adapters use TSET or
TT for an output clock and RxC as an input clock. Please note that TSET
(Transmit Signal Element Timing) is the EIA-530 equivalent of TT, the RS-232
signal Terminal Timing. For a loop-back plug connect the Transmit signal(s)
to the receive signal(s) and the TSET (EIA-530) or TT (RS-232) signal(s) to
the RxC signal(s).

  For Loop-Back Plug:

     For Single Ended (RS-232, MIL-188/114)
	Connect Tx to Rx
	Connect TSET or TT to RxC

     For Differential Interface (RS-530, V.35, MIL-188/C, etc.)
	Connect Tx+ to  Rx+
	Connect Tx- to  Rx-
	Connect TSET+ or TT+ to RxC+
	Connect TSET- or TT- to RxC-


Dip-Switch and Jumpers:

Note: If a jumper is not listed, that jumper is not relevant to this example.

    ACB-104             ACB-530             ACB-VI
	SW1 2,3,4,8 On      SW1 2,3,4,8 On      SW1 2,3,4,8 On
	E2 O                E8 0|0000           E9 A,B
	E1 A,B,D            E2 0|0000           E15 00||0000
			    E4 000000||         E16 000000||
			    E5 00||0000

    ACB-III             ACB-IV              ACB-V
	SW2 2,3,4 On        SW1 2,3,4 On        SW1 2,3,4 On
	E10 |00|            E2 00||0||00        E2 1,4
	E6  |0000|          E3 1,4              E1 1,4,6,7
	E4 1,4              E5 1,4,6,7          (See Note 3)
	E5 1,4,6
	E9 1

   Note 1: The ACB-II does not support Full-Duplex DMA (See file APP_NOTE.TXT)

   Note 2: The ACB-MP and MAXPORT do not support DMA transfers.

   Note 3: The ACB-V can only receive clocks. To use this example you will
	   either need to modify WR11 to receive transmit and receive clocks,
	   or contact technical support for a copy of the modification to
	   allow the ACB-V to source clocks. CCITT V.35 does not specify
	   a clock output.

BISYNC Note:

This example will transmit the test string ("THE QUICK BROWN FOX...") as a
BISYNC message. Note that this example does not transmit or check received
CRCs. If you wish to include CRCs in the data stream, the DMA terminal count
must be increased by 2. Please refer to the program DMA2.C for and example
of this modification. This difference is due to the 2 byte CRC that is
appended to each BISYNC message.

Implementations of BISYNC communications will vary on different computer
systems. It is very possible that you will need to modify this program
to work with another BISYNC application. In most BISYNC applications, the
enter hunt mode command is issued before a link is established.  This program
does not include a CRC on transmit or receive. DMA3.C is a very simple BISYNC
example and does not implement and link control protocol. Link protocols
differ on various implementations of BISYNC.

A typical BISYNC message has the following format:

    SYN SYN SOH Header STX Text ETX CRC

Where SYN is sync character, SOH is Start of Header Control Character, Header
is application specific message information, STX is Start of Text Control
Character, Text is the data to be transferred, ETX is End of Text Control
Character (ETB End Text Block can also be used), and CRC is the 16 bit
cyclic redundancy check generated by the SCC and checked by the receiver.
This example program does not send the SOH or Header Information.

BISYNC Communications, unlike SDLC or HDLC, relies on the application or
driver to maintain character synchronization. To ensure data integrity, the
message passing is usually half-duplex (in one direction at a time). Each
node will typically enter HUNT Mode after a message is transmitted. This may
be accomplished in a polling routine or in an Interrupt Service Routine (ISR).
When using the ISR method, the SCC can be programmed to generate and interrupt
on the transition of the SYNC/HUNT bit. Please note that when using BISYNC
communications, the SCC is not aware when character synchronization is lost.
For this reason the Enter Hunt Mode Command must be issued after the
transmission of each message (after the CRC). Please refer to the SCC users
manual for more detailed information on BISYNC Communications.


Build Dependencies:

DMA3.C
 * ACB.OBJ
 * ACB.H
 * DMA.OBJ
 * DMA.H
 * Z8530.H
 * ASCII.H (or EBCDIC.H) contains BISYNC control codes

 * Denotes that files are located in the \LIBRARY directory.