With the default settings, the terminal window emulates a 110 Baud Teletype, connected to a SCELBI with a SCELBI TTY interface. This interface interfaces with the SCELBI CPU with a single output latch for transmit and another for receive. This is often called "bit banged" I/O. The baud rate is completely under control of how fast the 8008 reads and writes bits to these ports. I have been able to write 8008 code that supports a baud rate of up to 2400 baud. The terminal supports baud rate settings of 110(default), 300, 1200 and 2400. MEA assumes a baud rate of 110. Output and input will not work, if the 8008 software and terminal settings do not match.
The terminal also optionally supports automatically issuing a line feed when a CR is encountered. MEA requires CR and LF to be issued separately from software.
The terminal defaults to the assumption that input and output data has the most significant bit set. The terminal setting can be changed using the menu, if software is encountered that uses different assumptions.
The memory menu allows configuring memory to 4k of system memory,
which is the maximum memory of the original SCELBI 8H. A
menu sub-option allows selection of 3.75 K bytes of emulated SRAM
along with an emulated 256 byte EPROM or 4K of emulated SRAM
with no EPROM. If the EPROM option is selected, a
small monitor, MCMON, is located at page 17. In this mode,
there is one additional option to consider. That is which
version of MCMON to install into page 17 EPROM. There are
three versions of MCMON available.
The tabs are located just below the panel switches.
The emulated hardware for interfaces are statically assigned to
I/O ports. When the system is configured for 4K of memory,
the port assignments are as follows.
| 4K MEMORY I/O
CONFIGURATION |
||
| Interface |
Output Port |
Input Port |
| Scopewriter | 10 - 13 |
|
| ASCII Keyboard |
14 (ack) |
4 (data in) |
| Audio Tape | 15 |
3 |
| TTY Bit Serial |
16 |
5 |
| Digital Group Video | 17 |
|
To emulate the SCELBI 8B, select the16K SRAM option. A menu
suboption allows selection of 12K SRAM along with 4K EPROM loaded
with MEA. When configured for 12K with MEA enabled, there is
one additional option to consider. That is which MEA driver
to install.
The tabs are located just below the panel switches.
The emulated hardware for interfaces are statically assigned to
I/O ports, as described in the MEA user manual. MEA software
can only use the TTY or the Oscilloscope/Keyboard interface at any
give time. When the system is configured for 16K of memory,
the port assignments are as follows. Note that there is no
MEA driver currently available for the Digital Group Video
interface, but emulated hardware is accessible to user developed
programs.
| 16K MEMORY I/O
CONFIGURATION |
||
| Interface |
Output Port |
Input Port |
| Oscilloscope | 10 & 11 |
|
| ASCII Keyboard |
12 (ack) |
4 (data in) |
| Audio Tape |
13 |
3 |
| TTY Bit Serial |
16 |
5 |
| Digital Group Video |
17 |
|
Memory can be zeroed out with the "Clear" command. This can be helpful when the system state is in a problematic mode. For instance SCELBAL assumes that the first command issued is "SCR". If "SCR" is not the first command issued, you may need to clear memory and reload SCELBAL to get it into a working state.
The load command allows you to load an Intel Hex formatted object file directly into emulated memory. Though this feature did not exist on real SCELBI mini-computers, this cheat is much faster than than loading through the cassette interface, which can take 5 minutes or longer to load a full memory image into a SCELBI-8B.
This menu, allows you to disable all and individual sound output from the SCELBI emulator. Note that the cassette playback sound is not perfectly synchronized to actual tape reads, but will give you an approximate idea of how the read is progressing. Tape sound output while recording is not currently implemented.