[Coco] FDD 26pin to 34pin

[Mike Pepe]

Chester A Patterson wrote:
> I think now I've got it gentlemen.
> Passing this info for your far more knowledgeable review and advice.
> 
> Coco FDD interface (Disto)	PC FDD interface		FDD
> 26pin (Citizen OSDC)
> ------------------------------------------------------------------------
> ------
> 1	Gnd				Gnd
> +5V
> 2	N/C				Density Select		INDEX
> 3	Gnd				Gnd
> +5V
> 4	N/C				N/C
> DRIVE SELECT 0
> 5	Gnd				Gnd
> +5V
> 6	N/C				N/C
> DRIVE SELECT 1
> 7	Gnd				Gnd
> +5V
> 8	INDEX				INDEX
> READY
> 9	Gnd				Gnd
> +5V
> 10	DRIVE SELECT 0		MOTOR ON DRIVE 0		MOTOR ON
> 11	Gnd				Gnd
> N/C
> 12	DRIVE SELECT 1		DRIVE SELECT 1		DIRECTION SELECT
> 13	Gnd				Gnd
> Gnd
> 14	DRIVE SELECT 2		DRIVE SELECT 0		HEAD STEP
> 15	Gnd				Gnd
> Gnd
> 16	MOTOR ON			MOTOR ON DRIVE 1
> WRITE DATA
> 17	Gnd				Gnd
> Gnd
> 18	DIRECTION SELECT		DIRECTION SELECT
> WRITE GATE
> 19	Gnd				Gnd
> Gnd
> 20	HEAD STEP			HEAD STEP
> TRACK 00
> 21	Gnd				Gnd
> Gnd
> 22	WRITE DATA			WRITE DATA
> WRITE PROTECT
> 23	Gnd				Gnd
> Gnd
> 24	WRITE GATE			WRITE GATE
> READ DATA
> 25	Gnd				Gnd
> Gnd
> 26	TRACK 00			TRACK 00
> SIDE 1 SELECT (HS)
> 27	Gnd				Gnd
> 28	WRITE PROTECT		WRITE PROTECT
> 29	Gnd				Gnd
> 30	READ DATA			READ DATA
> 31	Gnd				Gnd
> 32	DRIVE SELECT 3		HEAD SELECT
> 33	Gnd				Gnd
> 34 	N/C				DISK CHANGE
> 
> The two FDD 26pin I have are from a TANDY 1400LT, they have the 0123
> switch onboard but the manual, from which I took the above info,
> mentions not the switches that I could find (they were set to 0 and 1
> when I yanked the drives) But the 1400 has a provision to add an
> external FDD and at the flip of a switch (on the side of the 1400) to
> make the external FDD either A or C drive.
> 
> So, I guess my lingering question is: where/how do I connect the Drive
> Select lines to the 26pin FDDs?
> 
> Thanks.
> 
> /Chester

The floppy drives use a bus topology. All signals go to all drives.

-Mike