Browse Prior Art Database

Multi Speed Control for Multi Mode SCSI I/O

IP.com Disclosure Number: IPCOM000014582D
Original Publication Date: 2002-Apr-01
Included in the Prior Art Database: 2003-Jun-19
Document File: 7 page(s) / 167K

Publishing Venue

IBM

Abstract

[Original SCSI I/O]

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Multi Speed Control for Multi Mode SCSI I/O

[Original SCSI I/O]

 Multi mode SCSI I/O consists of Low Voltage Differential (LVD) and Single End
(SE) type, which electrical specification are based on ANSI SCSI Parallel
Interface-3 (SPI-3). LVD supports up to a maximum of 15 SCSI devices on a 12m
flat cable. Data transfer rates is up to 160Mbyte/sec. LVD driver's waveforms
are shown in figure 1 and figure 2. Both functionality are properly. But from
the view point of timing margin, the heavy SCSI bus configuration (figure 2)
becomes bad.

           Fig.1 LVD Driver Waveform-1 ( 160Mbyte/sec, Cable=1.2m,#of
Hard Disk=1)

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         Fig.2 LVD Driver Waveform-2 ( 160Mbyte/sec, Cable=12m,#of Hard
Disk=15)

[ Proposed SCSI I/O]

 A speed controlled SCSI I/O is proposed in figure 3. SD1 controls slew rate
of driver. SD2 controls impedance. SR1 controls receiver noise filters. All
of three control pins work for both LVD and SE mode. According to the past
experiences, even if SCSI I/O meets SPI-3 spec, the functional failures
occurred at some user's application due to off spec of SCSI BUS configuration.
But it is very important to meet defact standard from the business point.

Each mode definition and a truth table is shown in table 4. Default mode of
driver and receiver meet SPI-3. Other modes are backup to meet defact
standard. User can select the best fitted speed mode by jumper pin or register
value in a chip.

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LVD Driver

Bias

Pre Driver Driver Base

Bias

Pre Driver Driver

SD1 SD2

Additional

Bias

Pre Driver

Driver

DriverPre DriverBiasBase

SE Driver

Fig.3 Schematic of Speed Controlled Driver

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LVD Receiver

RC Filter

RC Filter

SR1

RC Filter

SE Receiver

Fig.4 Schematic of Speed Controlled Driver

Table 1. Speed mode definition

I/O Mode SD1 SD2 SR1

                                        Comments
1st 0 0 X Default mode
2nd 1 0 X Backup (1)
3rd 0 1 X Backup (2)

4th 1 1 X Backup (3)
1st X X 0 Noise-preced
ing

2nd X X 1 Speed-preced
ing

[Hardware results of proposed SCSI I/O]

 Figure 5 an...