Ok, I didn't realize there was a distinction between the two. I see the word timer and I think they're equivalent.
The imagewriter uses 2 different clock rates, one for 9600 and 2400 baud, and one that's 1/8th that rate for 1200 and 300.
So I put a counter in for the other rate that basically delays the clock signal for 8 counts. That seems to work fine:
Here's c64 printing at 300 baud (seems to work on initial testing):
./mame c64 -user rs232 -user:rs232:rs232 imagewriter
100 OPEN 1,2,0,CHR$(6)
200 FOR A = 1 TO 20 : PRINT#1,"LINE";A;
210 FOR I=32 TO 96 : PRINT#1,CHR$(I); : NEXT I :
220 PRINT#1,"" : NEXT A
changing the baud rate dip switches, resetting the printer, and then
open 1,2,0,chr$(6) for 300 baud
chr$(8) for 1200 baud
chr$(10) for 2400 baud
(c64 doesn't support 9600 baud) (I think NI means not implemented)