Screen Device Specification

Memory Layout

Byte	Mode	Name	Description
00	R	X	error indicator
01-02	R	-	zero
03	R	Y	character count
04-06	R	-	zero
07	RW	Z	character

Operation

The program will contact the motherboard at [host:]port and register itself with the given address and interrupt. Then, the program will be ready to receive bytes and display them. Under Unix a Byte is displayed by sending it to the standard output. Whenever ready to receive a byte, it will signal an interrupt with the given interrupt number. At the given address it will provide a read/write octabyte in the format: given above.

The X byte signals errors. It will be 0x80 if an error occured and 0x00 otherwise. By setting the sign bit errors can be easily checked..

The Y byte contains the number of characters that were written to this address since the last output. This should be 0 if the address is ready to receive a character or 1 if the hardware is bussy with writing a byte. Any other value will indicate that characters were lost since the last write operation.

The Z byte contains the last character received. It is valid only if YY is not zero.

The complete ocatbyte will be reset to zero after a byte is output..

Configuration

The Screen has the following configurable parameters:

host	localhost	the host where the bus is located
port	9002	the port where the bus is located
address	default	address where the resource is located
interrupt	not set	interrupt sent when ready
x	0	the x position of the window
y	0	the y position of the window
minimized	false	start with a minimized window
debug	false	to generate debug output
debugmask	0xFFF0	set mask to hide debug output
verbose	false	make debugging verbose, sets debug mask to zero
define	not set	to define a name for conditionals
config	not set	filename for a configuration file
help	false	to print information

These can be set in default.vmb