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參數(shù)資料
| 型號： | MAXSMBUS |
| 廠商： | Maxim Integrated Products, Inc. |
| 英文描述： | 2-Wire Interface Board |
| 中文描述： | 2線接口板 |
| 文件頁數(shù)： | 2/8頁 |
| 文件大?。?/td> | 219K |
| 代理商： | MAXSMBUS |
E
2-Wire Interface Board
2
_______________________________________________________________________________________
SYMPTOM
CAUSE
SOLUTION
Can’t Find the Interface Board
Board not connected to
parallel printer port
Verify that the cable is a 25-pin parallel port I/O extension cable
with a plug on one end and a socket on the other end.
Verify that the cable is connected to a printer port, not a floppy
disk, SCSI, or serial communications port.
Clock or Data Stuck Low
Board is connected to cor-
rect port, but SMBus is not
functioning
Check power connections on the interface board.
Check clock and data signal connections.
Try operating the interface board without the companion Maxim
evaluation kit—this should cause the address-not-acknowledged
symptom described below.
Power Supply
The interface board is powered by a 78L05 linear regu-
lator. The companion board can draw about 20mA of
+5V power through the circuit protector. Companion
boards that require more power must provide their own
regulator. The unregulated input to the 78L05 is avail-
able on the right-angle header.
Fault-Protection Circuitry
Overvoltage fault protection is provided by a MAX367
fault protector (U7). If any of the SMBus interface sig-
nals exceed the MAX367’s power-supply rails, the
MAX367 increases its resistance to prevent damage to
the user’s computer. A MAX865 dual charge pump
(U6) and two zener diodes (D1 and D2) provide +7V
and -3V supplies to the MAX367, thus allowing 0 and
+5V signals to pass with a nominal resistance of 100
.
Bus Driving Circuitry
A 74HCT05 open-drain inverter (U1) is used to pull
down the SMBus interface signals. The 74HCT08 (U3),
74HCT74 (U4), and 74HCT04 (U2) buffer the signal to
the IBM PC and provide the capability to mask the
ALERT interrupts, detect an externally generated start
condition, and capture data sent by an external bus
master. Interface connections are listed in Table 1 and
Table 2.
Bus Monitoring Circuitry
Flip-flop U4A detects the start condition (falling edge of
SMBDATA when SMBCLK is high). Flip-flop U4B
detects the falling SMBCLK edge when enabled, and
U1F holds SMBCLK low until the software releases it.
To advance to the next data bit, the software uses U1A
to assert and then release SMBCLK. A logic high at the
input of U1A also resets flip-flop U4B. Because the IBM
PC parallel port has a limited number of inputs, the
start-detect circuit and the two alert inputs share a sin-
gle interrupt input. The source of the interrupt is distin-
guished using U3A, U3B, and U3C.
________________________________________________________Troubleshooting Guide
Address Not Acknowledged
SMBus is OK, but no
response at expected
SMBus address
Verify that the companion board is connected to the MAXSMBus
interface board.
Verify that the companion board is powered.
If the companion offers a choice of addresses, confirm that the soft-
ware and hardware addresses match. Some devices only read the
address select pins at device power-up.
Conflict with local printer
driver
Disable print manager in the Windows printer control panel. Disable
printer driver.
Operating system conflict
1) Use computer with commercially available BIOS.
2) Make a bootable floppy disk, remove unnecessary device dri-
vers from A:config.sys, and boot system from floppy.
Erratic Operation
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