The program that I like to use for a serial terminal is minicom. In order to configure minicom for communication with BUFFALO, at the command prompt enter minicom with the switch "s" followed by the name that you want to use for the setup configuration.
]$minicom -s /dev/ttyS0
I should note that the "/dev/ttyS0" dose not tell minicom to mount /dev/ttyS0. It is simply the name of the configuration that I have chosen; so as to remember which dev is mounted at the time minicom is ran normally. Once you are in the configuration mode you will have to set the baud rate and clear out the dialing strings. The baud rate for the BUFFALO monitor is 9600. There is no parity and one stop bit by default, this is what is needed. You will also need to change the ACSII file transfer string to include the switch "-c 10" at the end. I will explain the reason for this later.
There are a couple of assemblers for Linux. I have tried several different ones though I have had the most luck with as6811. The directives are slightly different then many other assemblers. I have some sample code and schematic here. to uses as6811 first make it with the included makefile. This will set asm in the local bin. So to run it you will have to be logged as a user. If you want it to be setup for the root user then you will have to modify the makefile. I'm not going to get into how to change that. In order to assemble code type asm and the file name at the user pronpt. NOTE: because the assembler was originally for DOS, and Linux is case sensitive the .asm quasi extension must be lower case.
]#asm MyCode.asm
Now, it may have come to your attention by now that minicom has to be ran by root and as6811 must be ran by a user. At least this is the default setup that I have. To get around this I generally use Xwindows logged on as a user. In the terminal window enter the command "su" then enter the password for root. I use this so that I can use a graphical text editor at the same time to edit the code.
Now for uploading the s19 file. BUFFALO uses plain ASCII to upload files. The ASCII transfer program that minicom uses dose not have any flow control. Though BUFFALO uses hardware flow control. The -c 10 switch tells the ASCII transfer program to go slow so that the flow control is not needed. In order to use the transfer program from within minicom after telling BUFFALO to load t, press control A then press S and select ASCII from the list. From there select the file to be downloaded. After that have fun debugging code and designing circuitry.