TMS279X datasheet(29/40 Pages) TI

29 / 40 page

TMS279X (WD279X) FLOPPY DISK FORMATTER / CONTROLLER FAMILY

status register

Upon receipt of any command, except the Force Interrupt command, the busy status bit is set and the rest of

the status bits are updated or cleared for the new command. If the Force Interrupt command is received

when there is a current command under execution, the busy status bit is reset, and the reset of the status

bits are unchanged. If the Force Interrupt command is received when there is not a current command under

execution, the busy status bit is reset and the rest of the status bits are updated or cleared. In this case,

status reflects the Type I commands.

The user has the option of reading the status register through program control or using the DRQ line with

DMA or interrupt methods. When the data register is read, the DRQ bit in the status register and the DRQ

line are automatically reset. A write to the data register also causes both DRQ's to reset.

The busy bit in the status may be monitored with a user program to determine when a command is complete,

in lieu of using the INTRQ line. When using the INTRQ, a busy status check is not recommended because a

read of the status register to determine the condition of busy will reset the INTRQ line.

The format of the status register is shown below:

(BITS)

Status varies according to the type of command executed as shown in Table 4.

Because of internal sync cycles, certain time delays must be observed when operating under programmed

1/0. They are: (times double when clock = 1 MHz).

OPERATION

NEXT OPERATION

DELAY REG’D

MFM

Write to Command Register

Write Any Register

Read Busy Bit (Status Bit 0)

Read Status Bits 1-7

Read from Different Register

12 µs

28 µs

6 µs

14 µs

IBM 3740 format - 128 bytes/sector

Shown below is the IBM single-density format with 128 bytes/sector. In order to format a diskette, the user

must issue the Write Track command, and load the data register with the following values. For every byte to

be written, there is one data request.

TMS279X Datasheet(PDF) 29 Page - Texas Instruments