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3. THEORY OF OPERATION
This chapter presents an operational overview of the hardware operation of the
ZT 8954. Each of the board's functions is described in detail. Frequently asked
questions are addressed below.
FREQUENTLY ASKED QUESTIONS
Why is the ZT 8954 Incompatible With Older CPU Boards?
The ZT 8954 relies upon the host CPU to perform DMA transfers between the floppy
disk controller and the host CPU's memory. Only boards that can field requests from a
DMA slave (for example, ZT 8902) can be used with the ZT 8954. Many older CPU
boards do not have on-board DMA controllers or do not allow for off-board DMA slaves.
With STD 32, DMA capability was added by defining the backplane signals necessary
for data transfer completion under DMA. The ZT 8954 is not supported by the ZT 8801,
ZT 8802, ZT 8808, ZT 8809, ZT 8816, ZT 8817, ZT 8901, ZT 8902 Revision 0.X, or
ZT 8911 Revision 0.X.
What Floppy Disk Drives are Supported by the ZT 8954?
The ZT 8954 supports all floppy disk drives that are compatible with the IBM-PC family.
Data transfer rates of 250 Kbps through 2 Mbps are supported. In addition, the ZT 8954
supports tape drive units that are floppy interface compatible, such as the Colorado
Memory Systems "JUMBO" tape drives.
How Do I Use Frontplane DMA?
The ZT 8954 is capable of frontplane DMA, but only as a special option from Ziatech
(ZT 8954-D3). The connector location for frontplane DMA is located underneath the
integrated 3½" drive. In order to minimize slot usage by the floppy subsystem, this
connector is not loaded. Frontplane DMA is primarily used for floppy operation in STD-
80 card cages that have no backplane DMA capability. When the frontplane DMA
connector is loaded, the floppy disk drive must be raised; this causes the complete
ZT 8954/Floppy Disk Drive to occupy two card slots.
How Do I Remote Mount A Floppy Disk Drive?
Floppy Disk Drives can be remote mounted with a ZT 8954-D0 board and the addition
of two cables, ZT 90077 and ZT 90172. These cables allow for interfacing drives up to
20" away from the controller. These cables support 3½" and 5¼" drives with separate
power connectors and drives that use the older style .050" ribbon cable for floppy drive
control (34-pin 0.1" connectors). The micro-floppy 3½" drives that use FPC cable are
not supported by this mechanism. These drives can be interfaced with a 26-pin FPC
cable on 1 millimeter pitch at up to 0.5 meters or less. Parlex company (telephone
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