Virtual Net 96 (VN96) Doc v1.0, 1996 by Hage & Steve of Wizcat
Version: 1.0, 12.03.1997
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Contents
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1.) Introduction
2.) General things
2.1) Devices
2.2) Installation & Handling
2.3) Do it yourself devices
3.) How to write own programs
3.1) Basics
3.2) The routine pack VN96ROUT.ASM
3.3) Asynchronous and synchronous
3.4) The first program
3.5) Synchronous programming
4.) Contact 1.) Introduction The Virtual Net 96 is a combination of hard- and software developed by us to connect two or more CPCs in a kind of network.
The Hardware consists of very simple devices connected to each CPC. These devices are linked to each other with normal cables.
The software consists of utilities or games accessing a routine pack developed by us. This routine pack makes it possible to transfer data with a speed of 60000 Baud.
This documentation introduces into the VN96 and teaches you how to write own VN96 programs.
You can skip section 3 if you don't want to create own programs, programmers should read the whole document. 2.) General things 2.1) Devices Devices and cable can be ordered from us (or buildt by yourself, see below): * Single cable
1 cable ;1.50 DM * Single device
1 device ; 4.50 DM * 'Add-On'
1 device and 1 cable ;6.00 DM * 'Beginner Set'
2 devices and 1 cable ;10.00 DM 2.2) Installation & Handling The devices are put into the printer port, the switch upwards.
Two pins at a time (one on the top of the other) belong together and must
be connected with the end of a cable. The marked wire (knot) belongs to the
upper pin. The other end of the cable has to be connected to another device.
The other two pins are used to connect a further device and so on.
If the switch is in position left the device is deactivated, in position
right it is activated. IMPORTANT: Is the CPC switched off or if there's no VN96 program active then
the device HAS TO BE DEACTIVATED (switch in position right)! If a program
has been started you can switch on the device and the program will handle
the rest. 2.3) Do it yourself devices For users familiar with a soldering iron, here's the wiring diagram of the
devices:
---------------------o--------------------------------------- Data ---------------------|-----------------o--------------------- GND
; | ; |
; / ; |
; Switch /---| ;|
;/ ; |
; | ; |
Resistor | ; |
10k o-------+ ;|
; | / | ;|
+-----+ |/ ;| ;|
+-----| |-----< | ;|
| +-----+ | ;| ;|
| ; | --------|---------o
| ; | ;|
| ; Transistor | ;|
| ; BC 547C | ;|
| ; | ;|
______ ; ____
Strobe ; Busy GND
(Pin 1) ; (Pin 11) (Pin 19 or another GND pin)
The pins are related to the printer port. Our devices and cables are assembled with an unique design. To maintain compatibility it is recommended to use the following specifications: * The connection of a device with a cable is provided with 1.3mm pins.
There sould be four pins, two data and two GND pins. * The data pins should be placed above, the GND pins below (to avoid a reversed connection) * The cables end in 1.3mm sockets and on both ends of the cable the same of the two wires is marked with a knot. * Switch: position right: off, position left: on If you can't imagine how this looks like you can lend devices and wires from us for free. 3.) How to write own programs 3.1) Basics The data wire has two states, one and zero. This state can be requested with the 6th bit of the I/O address #F500 (Busy), for example: IF INF(&F500) > 64 THEN PRINT "One!" ELSE PRINT "Zero!" Or with Z80: LD B,#F5
IN A,(C)
CP 64
JR NC,one
JR zero This state always is equal on all connected CPCs, meaning the state is either one or zero on ALL CPCs. A CPC can influence this state with the 7th bit of the I/O address #EF00: OUT &EF00,128 ' Put data wire to one
OUT &EF00,0 ' Put data wire to zero Here an example with Z80 too: LD BC,#EF80 ' Put data wire to one
OUT (C),C
LD B,#EF00 ' Put data wire to zero
OUT (C),A But what happens if a CPC puts the wire to one and another puts it to zero?
Against expections the devices doesn't disintegrate or explode or something like that. The usual state of the data wire is one. If one or more CPCs put a zero to the wire the whole wire switches to zero. That means zero has priority above
one, the 'ones'of other CPCs are ignored. To say it in a different way: The wires only switches to one if ALL CPCs put a one to the wire. This is the only way to realize a bidirectional connection. Apart from that it is very useful for synchonisations (see below).
IMPORTANT: The first command in every VN96 program (in the BASIC loader, for example) must put the data wire to one. After a reset the printer port puts the data wire to zero and that would block a transmission. That's why the device has to be switched off when there's no VN96 program running. But the user switches on the device after he has started a VN96 program, therefore each VN96 program has to put the data wire to one as soon as possible.
A transmission runs off like this: All CPCs willing to receive put the data wire to one and now the CPC that wants to send can influence the wire according to the bits he wants to transmit. But this routines must not be written again, because there is... 3.2) The routine pack VN96ROUT.ASM The routines of the routine pack VN96ROUT.ASM (which should be on the same disk as this doc, the newest version is available from us for free) are as follows: vnsnd Transmit a byte
vnrec Receive a byte
vnsndb Transmit a data block
vnrecb Receive a data block
vnzero Wait for zero
vnone Wait for one
vnzeri Wait for zero without timeout
vnonei Wait for one without timeout
vnwait Wait a determined time
vnwais Wait for a request routineIMPORTANT: All routines do not change the interrupt state. But if a routine is executed the interrupts MUST be disabled (DI). Here the routines in detail: Routine: 'vnsnd', transmit a byte
---------------------------------------
Jump in: A=Byte to transmit
Jump out: A, BC destroyed
Comments: Byte is immediately transmitted without checking the wire. Routine: 'vnrec', receive a byte
--------------------------------------
Jump in: -
Jump out: CY=0 --> Ok, A=received byte
; CY=1 --> Timeout error
; A, BC, DE destroyed
Comments: If there's no byte received within ca. 1s the routine returns with CY=1. Routine: 'vnsndb', transmit a data block
----------------------------------------------
Jump in: HL=Pointer to the data block
; DE=Length of the data block in bytes
Jump out: A, BC, DE, HL destroyed
Comments: Data block is immediately transmitted without checking the wire. Routine: 'vnrecb', receive a data block
---------------------------------------------
Jump in: HL=Pointer to a buffer
Jump out: CY=0 --> Ok, (HL)=data block
; DE=length ot the data block in bytes
; CY=1 --> Timeout error
; A, BC, DE, HL destroyed
Comments: If there's no data block received within ca. 1s the routine returns with CY=1. Routine: 'vnzero', wait for zero state
--------------------------------------------
Jump in: -
Jump out: CY=0 --> Data wire is zero
; CY=1 --> Timeout error
; A, B, DE destroyed
Comments: If the data wire doesn't switch to zero state within ca. 1s the routine returns with CY=1. Routine: 'vnone', wait for one state
------------------------------------------
Jump in: -
Jump out: CY=0 --> Data wire is one
; CY=1 --> Timeout error
; A, B, DE destroyed
Comments: If the data wire doesn't switch to one state within ca. 1s the routine returns with CY=1. Routine: 'vnzeri', wait for zero state without timeout
------------------------------------------------------------
Jump in: -
Jump out: Data wire is zero
; A, B, DE destroyed
Comments: This routine returns only if the data wire is in zero state. Routine: 'vnonei', wait for one state without timeout
-----------------------------------------------------------
Jump in: -
Jump out: Data wire is one
; A, B, DE destroyed
Comments: This routine returns only if the data wire is in one state. Routine: 'vnwait', wait a determined time
-----------------------------------------------
Jump in: HL=Wait time in 7.63us steps
Jump out: A, HL destroyed
Comments: Waits HL*7.63 micro seconds.
; Rule of thumb: 9 HL cycles are one raster line. Routine: 'vnwais', wait for a request routine
---------------------------------------------------
Jump in: -
Jump out: -
Comments: Waits the time the routines vnzero, vnone, vnzeri and vnonei need to notice a change of the data state. 3.3) Asynchronous and synchronous Gererally, two techniques are distinguished between: asynchronous and synchronous.
Asynchrounous means simply: nothing happens - nothing is transmitted. A chat program is an example for this. The data wire is normally in one state. If one of the chatters presses a key, the keycode is transmitted to the other CPCs and after this the wire swichtes to one again.
But why is the standard state one instead of zero? As sayed above: Well, if one or more of the CPCs put the wire to zero, none of the others could change this state any more.
Synchronous means: The connected CPCs have a determined order and data is contiuously exchanged. Example: The Tron-like game 'Last Action Point' by Steve of Wizcat. During the game bytes are continously exchanged between the
CPCs in a determined order. These bytes contain the joystick information of each player. After a sychronization phase player one sends his byte, then player two sends his byte, then player three and so on. After this all CPCs have to calculate the exchanged data, display graphics, etc. Then the game leads into a new sychronisation phase.
But now we have a problem: The single CPCs do not all need the same time to process their data. That's why the transmissions have to be synchonisized.
To this matter there is a simple but important solution named synchronization phase:
After the transmission of all bytes all CPCs put the data wire to zero and start their calculations. If a CPC has finished this he puts the wire to one again. But the wire won't switch to one unless ALL CPCs put the wire to one. Therefore the CPC must wait until the wire swiches to one. All CPCs will return synchronous from this request, when the last CPC puts the wire to one. Then the new transmission can begin. 3.4) The first programm As an example for asychronous programming a chat program was mentioned above. Now such a chat program will be developed step by step.
First of all the wire must be put to one to avoid blocking transmissions: ORG #A000
chatstart: LD BC,#EF80 ; put data wire to one
OUT (C),C Now follows the main loop which checks if another CPC would like to transmit any byte: mainloop: LD B,#F5 ; check data wire
IN A,(C)
CP 64 ; is it zero?
JR C,recabyte ; yes, --> receive byte Is the wire in zero state the program jumps to the routine which receives the byte. If noone sends a byte, the keyboard is checked: CALL #BB09 ; key pressed?
JR C,sndabyte ; yes, --> transmit byte
JR mainloop If there a key is pressed the program jumps to the transmit routine. If not the loop starts again.
Here's the routine to receive a byte using the routine pack VN96ROUT.ASM: recabyte: DI ; disable interrupts
CALL vnone ; wait for one state
JR C,mainloop ; timeout error, --> back to the main loop
CALL vnrec ; receive the byte
JR C,mainloop ; timeout error, --> back to the main loop
CALL #BB5A ; print the char
JR mainloop ; back to the main loop The routine waits for the end of the start bit and then receives and prints the byte.
Now follows the routine which transmittes a byte when a key is pressed: sndabyte: DI ; disable interrupts
LD I,A ; save the byte
LD BC,#EF00 ; send the start bit
OUT (C),C
LD HL,1500 ; wait for the others to notice it
CALL vnwait
LD BC,#EF80 ; quit the start bit
OUT (C),C
CALL vnwais ; wait for the others to notice it
LD A,I ; transmit the byte
CALL vnsnd
LD A,I ; print the char
CALL #BB5A
JR mainloop ; back to the main loop Here the start bit and then the byte is transmitted. The first wait loop is required because the other CPCs need a litte time to leave the main loop (maybe in the middle of a #BB09 call). The second wait loop 'vnwais'gives the CPCs time to return from their 'vnone' call. 3.5) Synchronous programming As example for synchronous programming Steve of Wizcats 'Last Action Point' is used here.
To use synchron programming the CPCs must have a determined order. This is reached with a asynchronous 'chat' between the players at the beginning of the game, the chat phase.
Every CPC calculates a random number. At the start on all CPCs the program is loaded and the data wire is in one state. Now one player presses the start key. This CPC transmittes a start bit (see 3.4) which starts the chat phase. Now every CPC counts down his random number. If a CPC counts out he transmittes a start bit followed by his player informations (name, points etc.). The CPCs must therefore check the data state while counting down their random numbers.
So the single CPCs one after the other transmit their data. While doing this increasing player numbers are assigned determining the order of the CPCs.
To quit these phase the random numbers must be restricted in its size. If the time according to the largest possible random number is ran out the chat phase can be quitted. No other CPC will send any data.
The chat phase is now followed by a sychnonisation phase leading into synchonous mode (see 3.3). 4.) Contact For free software, questions, critics, suggestions, to order devices or just for fun write to: * Hage of Wizcat
Abt-Rudolfstr. 46
73479 Pfahlheim
E-Mail: wsteng@rzws.fh-aalen.de * Steve of Wizcat
Ihnbergstr. 9/1
73479 Pfahlheim
E-Mail: Christian.Stengel@T-Online.de
;csteng@rzws.fh-aalen.de * http://www.home.pages.de/~vn96 
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