Tandy 1400LT - VFO and FDC Interface

The drive assignment is switchable by the BOOT SELECT Switch (SW3)
The following are drive assignments.
3.5 inch boot
5.25 inch boot
DRIVE 1
DRIVE A DRIVE
C
DRIVE 2 DRIVE B DRIVE B
EXT FDD DRIVE C DRIVE A
CLK li
MFM zg
WINDOW .$:
WCLK
RDATA
SYNC
VFO (DATA SEPARATOR FOR FDD)
The VFO (IC57) is a CMOS VFO data separator for use in the floppy disk interface. The VFO removes bit phase
shift origination in variations in disk rotation speed or peak shifts from disk drive read data to generate data
window and reproduces read data pulse signals for output to a floppy disk controller. It provides the following
outputs as FDC clocks. CLK1:
4MHz, WCLK (Write clock): 5.25 inch MFM Interval T = 2usec.
Figure 4-26 shows VFO and FDC interface.
+5v
-4
3LK1 MIN/sm l1
19. WCLK
lo MFM/ RDATA READ DATA
6 .22
5 SYNC :EG -zO
9 DATA TIMOU~
~ WINDOW CLK2
-
VFO ( SED9420CAC 1
$10, lM
16. OMHz
Figure 4-26. VFO and FDC Interface
4-38