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DS2490
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These six settings are controllable with discrete Mode commands or as embedded command/parameter
values in Communications commands.
As listed in Table 5 and summarized previously, there are eight Mode commands. The USB control
transfer setup packet coding to transmit these commands is detailed in Appendix 3. Mode commands are
immediately processed by the DS2490 when they are received. The DS2490 power-on default values for
these parameters are as listed in Table 12. Each command and parameter control is detailed in the
following paragraphs.
Mode Command Set Summary Table 5
Command
Function
ENABLE PULSE
Enable/disable 1-Wire strong pullup pulse to 5V and/or +12V programming
pulse.
ENABLE SPEED
CHANGE
Enable/disable dynamic change of the 1-Wire speed through a
communication command.
1-WIRE SPEED
Communication speed of the 1-Wire bus.
STRONG PULLUP
DURATION
Duration of 1-Wire strong pullup.
PULLDOWN SLEW
RATE
Slew rate of 1-Wire pulldown.
PROG PULSE
DURATION
Duration of 1-Wire VPP EPROM programming pulse.
WRITE-1 LOW TIME
Duration of 1-Wire Write-1 low time.
DSOW0 RECOVERY
TIME
Recovery time for the 1-Wire data sample offset / Write-0 transaction.
Mode Command Set Descriptions:
ENABLE PULSE—This command is used to enable or disable a 1-Wire strong pullup pulse to 5V
and/or +12V EPROM programming pulse. Two bit positions in the parameter byte are used to control the
enabled/disabled state for each pulse type. The specific pulse is enabled when the respective bit is set to a
1 and disabled when set to a 0. The DS2490 power-up default state for both strong pullup and
programming pulse is disabled.
ENABLE SPEED CHANGE—This command is used to enable or disable a 1-Wire communication
speed change. Enabled when a TRUE parameter value is passed with the command, disabled with a
FALSE. The DS2490 power-up default state for speed change is disabled.
1-WIRE SPEED—This command is used to set the speed of 1-Wire communication; three settings are
possible. The parameter codes to select the desired or required speed are as listed in Table 6. As shown,
speed codes 0x3..0xF are undefined. The DS2490 decodes the 3 LSBs of the 1-Wire speed code. Sending
a code other than the defined values in Table 6 will result in undefined behavior. The DS2490 power-up
default communication speed is regular.