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82077AA-1

CHMOS SINGLE-CHIP FLOPPY DISK CONTROLLER

Intel 

82077AA

Table 1 82077AA Pin Description (Continued)

Symbol Pin I O

Description

HOST INTERFACE (Continued)

IDENT

27

I IDENTITY Upon Hardware RESET this input (along with MFM pin) selects

between the three interface modes After RESET this input selects the type of

drive being accessed and alters the level on DENSEL The MFM pin is also

sampled at Hardware RESET and then becomes an output again Internal pull-

ups on MFM permit a no connect

IDENT MFM INTERFACE

1

1 or NC AT Mode

1

0

ILLEGAL

0

1 or NC PS 2 Mode

0

0

Model 30 Mode

AT MODE Major options are enables DMA Gate logic TC is active high

Status Registers A B not available

PS 2 MODE Major options are No DMA Gate logic TC is active low Status

Registers A B are available

MODEL 30 MODE Major options are enable DMA Gate logic TC is active

high Status Registers A B available

After Hardware reset this pin determines the polarity of the DENSEL pin IDENT

at a logic level of ‘‘1’’ DENSEL will be active high for high (500 Kbps 1 Mbps)

data rates (typically used for 5 25 drives) IDENT at a logic level of ‘‘0’’

DENSEL will be active low for high data rates (typically used for 3 5 drives)

INVERT is tied to ground

DISK CONTROL (All outputs have 40 mA drive capability)

INVERT

35

I INVERT Strapping option Determines the polartity of all signals in this section

Should be strapped to ground when using the internal buffers and these signals

become active LOW When strapped to VCC these signals become active high

and external inverting drivers and receivers are required

ME0

ME1

ME2

ME3

57 O ME0–3 Decoded Motor enables for drives 0 – 3 The motor enable pins are

61

directly controlled via the Digital Output Register

63

66

DS0

58 O DRIVE SELECT 0 – 3 Decoded drive selects for drives 0 – 3 These outputs are

DS1

62

DS2

64

decoded from the select bits in the Digital Output Register and gated by

ME0 – 3

DS3

67

HDSEL

51 O HEAD SELECT Selects which side of a disk is to be used An active level

selects side 1

STEP

55 O STEP Supplies step pulses to the drive

DIR

56 O DIRECTION Controls the direction the head moves when a step signal is

present The head moves toward the center if active

WRDATA 53

O WRITE DATA FM or MFM serial data to the drive Precompensation value is

selectable through software

WE

52 O WRITE ENABLE Drive control signal that enables the head to write onto the

disk

5

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