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Technical Reference Guide
Compaq Deskpro EN Series of Personal Computers
Desktop and Minitower Form Factors
Third Edition - September 1998
5-1
Chapter 5
INPUT/OUTPUT INTERFACES
5.
Chapter 5 INPUT/OUTPUT INTERFACES
5.1
INTRODUCTION
This chapter describes the standard (i.e., system board) interfaces that provide input and output
(I/O) porting of data and specifically discusses interfaces that are controlled through I/O-mapped
registers. The I/O interfaces are integrated functions of the south bridge (82371) and the I/O
controller (87307). The following I/O interfaces are covered in this chapter:
♦ Enhanced ID interface (5.2) page 5-1
♦ Diskette drive interface (5.3) page 5-9
♦ Serial interfaces (5.4) page 5-14
♦ Parallel interface (5.5) page 5-20
♦ Keyboard/pointing device interface (5.6) page 5-27
♦ Universal serial bus interface (5.7) page 5-34
5.2
ENHANCED IDE INTERFACE
The enhanced IDE (EIDE) interface consists of primary and secondary controllers (integrated
into the south bridge component) that can support IDE devices each. Devices that may connect to
the IDE interface include hard drives, CD-ROM drives, PD-CD-ROM drives, and 120-MB
floptical drives.
Two 40-pin keyed IDE data connectors (one for each controller) are provided on the system
board. Each connector can support two devices and can be configured independently for PIO
modes 1-4, DMA modes 1-2, or Ultra ATA modes 0-2. In standard configuration an IDE drive is
attached to the primary connector and the CD-ROM (if installed) is attached to the secondary
connector.
NOTE:
With only one device connected to a controller, a 40-conductor cable 10 inches
or shorter will allow UATA mode 2 operation. Two devices on the same 40-pin/10”cable
will limit operation to UATA mode 1 (25 MB/s). For a controller to provide UATA
mode 2 operation with two devices connected requires an optional 80-conductor cable.
Pin 34 is used by BIOS for 40-/80-conductor cable detection. On the 40-conductor cable,
pin 34 is high (+5 VDC). On the 80-conductor cable, pin 34 is low (grounded).
5.2.1
IDE PROGRAMMING
The IDE interface is configured as a PCI device and controlled through standard I/O mapped
registers.