2400 Baud Cassette, 300 Baud TTY for N2
Here is a very simple mod for Nascom 2 owners to give cassette
I/O at 2400 Baud.
Connect TP20 to TP4 and TP21 to TP5. If you now select external
UART clock you have the cassette interface running at 2400 Baud.
The switch settings of LSW2 are :–
where switches 1, 2 and 3 select the transmission speed to the cassette
and 4, 5 and 6 the receiving speed from the cassette. Switch 7 should
be down to select cassette input. (Up selects TTY input.)
To make 300 Baud TTY available is a little more difficult but
since many acoustic couplers and teletype devices work at this speed it
may be necessary. Transmission is the easiest since only the clock
speed of the transmission side of the UART needs setting and this is
readily achieved by the existing switches on LSW2.
|and with the mod above|
Reception cannot be achieved in the same way because the UART
receive clock for tape is derived from a Phase Lock Loop (PLL). The TTY
input must have a ‘hard’ clock, as the PLL can not regenerate the clock
from the incoming TTY signal. Therefore, to get different receive
speeds for TTY Input the appropriate clock signals must be gathered
from various places and applied to the UART. This may be done by
connecting the required clock from the input side of the transmit speed
selection switches to the external receive clock input (TP5). The most
usual TTY speed required is 300 Baud and the clock for this may be
picked up from I1C32 Pin 4 with LSW2 switch 1 down or from IC31 Pin 9. A
switch will then be required to select between the 2400 Baud cassette
clock (coming from the PLL circuit) and the 300/1200/2400 Baud TTY
clock going into the external receive clock input (TP5).