In some cases a user may have the need to communicate with the ELLO computer via a serial console. Such functionality is supported by the system software, and provided on the same port pins as the PS/2 keyboard, so both are mutually exclusive. On power up the system checks whether there is a PS/2 keyboard connected, and if there is no keyboard detected, switches automatically in console mode.
The console mode uses a fixed serial protocol (TTL signal levels) on the purple mini-DIN connector, normally allocated for a keyboard.
Just like the keyboard, a serial console uses the same pins 1, 3, and 5 on the connector for communication.
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Pin 1: PS/2 keyboard data, or TxD channel from ELLO to the console |
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Pin 3: Common ground 0V |
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Pin 5: PS/2 keyboard clock, or RxD channel from the console to ELLO |
If the system is built around a PIC32MX270 chip, serial console is also available on the USB channel.
The serial console works with a fixed protocol 38400 bauds, 8 bits data length, no parity, 1 stop bit (otherwise said “8N1”). The speed is chosen as a reasonable compromise to accommodate the vast majority of possible terminal devices connected to the ELLO.
The serial console works only with text output, and has no defined size for the screen. The video output from the system is still available, provided there is a monitor connected on the video port.
A system with no display gains about 15% in increased computational performance due to the fact the processor is freed from the tasks associated with generation of a video signal. It also makes use of the reserved video RAM, so there is more memory available for user programs.