HP dc7900 manual Keyboard/Pointing Device Interface, Keyboard Interface Operation

Models: dc7900

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Input/Output Interfaces

5.6Keyboard/Pointing Device Interface

The keyboard/pointing device interface function is provided by the SIO controller component, which integrates 8042-compatible keyboard controller logic (hereafter referred to as simply the “8042”) to communicate with the keyboard and pointing device using bi-directional serial data transfers. The 8042 handles scan code translation and password lock protection for the keyboard as well as communications with the pointing device.

5.6.1 Keyboard Interface Operation

The data/clock link between the 8042 and the keyboard is uni-directional for Keyboard Mode 1 and bi-directional for Keyboard Modes 2 and 3. (These modes are discussed in detail in Appendix C). This section describes Mode 2 (the default) mode of operation.

Communication between the keyboard and the 8042 consists of commands (originated by either the keyboard or the 8042) and scan codes from the keyboard. A command can request an action or indicate status. The keyboard interface uses IRQ1 to get the attention of the CPU.

The 8042 can send a command to the keyboard at any time. When the 8042 wants to send a command, the 8042 clamps the clock signal from the keyboard for a minimum of 60 us. If the keyboard is transmitting data at that time, the transmission is allowed to finish. When the 8042 is ready to transmit to the keyboard, the 8042 pulls the data line low, causing the keyboard to respond by pulling the clock line low as well, allowing the start bit to be clocked out of the 8042. The data is then transferred serially, LSb first, to the keyboard (Figure 5-6). An odd parity bit is sent following the eighth data bit. After the parity bit is received, the keyboard pulls the data line low and clocks this condition to the 8042. When the keyboard receives the stop bit, the clock line is pulled low to inhibit the keyboard and allow it to process the data.

Start

D0

D1

D2

D3

D4

D5

D6

D7

Parity

Stop

Bit

(LSb)

 

 

 

 

 

 

(MSb)

 

Bit

0

1

0

1

1

0

1

1

1

1

0

Data

Clock

Th

Tcy

Tcl Tch

 

Tss Tsh

 

 

Parameter

Minimum

Maximum

 

 

Tcy (Cycle Time)

0 us

80 us

 

 

Tcl (Clock Low)

25 us

35 us

 

 

Tch (Clock High)

25 us

45 us

 

 

Th (Data Hold)

0 us

25 us

 

 

Tss (Stop Bit Setup)

8 us

20 us

 

 

Tsh (Stop Bit Hold)

15 us

25 us

Figure 5-6. 8042-To-Keyboard Transmission of Code EDh, Timing Diagram

Control of the data and clock signals is shared by the 8042 and the keyboard depending on the originator of the transferred data. Note that the clock signal is always generated by the keyboard.

After the keyboard receives a command from the 8042, the keyboard returns an ACK code. If a parity error or timeout occurs, a Resend command is sent to the 8042.

 

Technical Reference Guide

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HP dc7900 manual Keyboard/Pointing Device Interface, Keyboard Interface Operation

dc7900 specifications

The HP dc7900 is a well-regarded desktop solution that serves as a testament to HP's commitment to performance, reliability, and user accessibility. Introduced as part of HP’s Compaq line and designed primarily for business professionals, the dc7900 combines powerful processing capabilities with a compact form factor that suits various office environments.

One of the standout features of the HP dc7900 is its robust configuration options. It typically comes equipped with Intel's Core 2 Duo or Quad processors, giving users the ability to handle demanding applications seamlessly. The inclusion of Intel's technologies, such as Intel vPro, enhances remote management and IT control, making it an ideal choice for businesses looking to streamline their operations.

The dc7900 is designed with flexibility in mind. It offers multiple form factors, including mini-tower, small form factor, and ultra-slim desktop configurations. This variety enables organizations to choose a model that best fits their workspace requirements, maximizing both efficiency and aesthetics. The small footprint models are particularly beneficial in space-constrained environments, while the mini-tower version provides expandability for future upgrades.

In terms of graphics capabilities, the HP dc7900 typically features integrated Intel graphics, with options to install discrete graphics cards for users who require enhanced visual performance. This makes the dc7900 suitable for tasks ranging from standard office applications to more graphics-intensive responsibilities.

Connectivity is another key characteristic of the HP dc7900. It is equipped with a variety of ports, including USB 2.0 and audio jacks, allowing users to connect peripherals easily. Additionally, the dc7900 supports legacy connections, making it easier for businesses with older equipment to integrate new systems without hassle.

Durability and reliability are hallmarks of the HP dc7900. Built with high-quality materials and subjected to rigorous testing, this desktop is designed to withstand the demands of a bustling office environment. Furthermore, HP's comprehensive warranty and support options assure businesses of the reliability of their investment.

The HP dc7900 is not just a powerful desktop; it’s a versatile and dependable solution for modern businesses. With its combination of performance, expandability, and solid build quality, the dc7900 remains a relevant choice for those looking to enhance their productivity and efficiency in the workplace.