DS1481S Maxim Integrated Products, DS1481S Datasheet - Page 3

• Manufacturer Part Number: DS1481S
• Description: IC BUS MASTER 1 WIRE 14-SOIC
• Manufacturer: Maxim Integrated Products

Specifications of DS1481S

• Interface: 1-Wire
• Voltage - Supply: 2.7 V ~ 5.5 V
• Package / Case: 14-SOIC (3.9mm Width), 14-SOL
• Mounting Type: Surface Mount
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Applications: -

DS1481
If after 480μs of low time the I/O line did not return high, either the I/O line has been shorted to ground
or there is at least one 1-Wire device connected to the I/O line which is issuing an alarm interrupt (see
Figure 6). In this case the DS1481 waits for I/O to return high for an additional 3840μs (64 * 60). If time
expires the I/O line is assumed to be shorted and the DS1481 releases O1/BSY1 and O2/BSY2. If the I/O
line returns high, the DS1481 continues to monitor the presence detect portion of the reset (as described
above) as for the non-interrupt case. Note that the 3T idle high time is still required after the presence
detect ends.
OVERDRIVE
The DS1481 also supports overdrive communication with overdrive capable 1-Wire devices. When the
DS1481 powers up it is in normal mode (i.e., OD = 0, Figure 1). To toggle to overdrive mode the host
sets D/CLK and RES low and drives ENI low. The DS1481 toggles the OD bit to a logic high and returns
the states of I1 and I2 on O1/BSY1 and O2/BSY2. Overdrive mode is cleared in the same way. When
overdrive is turned off (OD = 0). O1/BSY1 and O2/BSY2 are driven low to report the state of the OD bit.
When OD = 1, communication with the 1-Wire device is exactly as described in the operation section
above. The actual 1-Wire timing for both modes of operation is described in Figures 4, 5, and 6.
Note that when toggling the OD bit there is no change on the I/O line.
PRINTER COEXISTENCE
In order to coexist with parallel port printers, the DS1481 utilizes two input pins (I1 and I2) and two
output pins (O1/BSY1 and O2/BSY2). When ENI is low these pins are used for transmitting data
received on the I/O pin or for issuing an unmistakable busy signal. When ENI is inactive (high) O1/BSY1
and O2/BSY2 propagate the states of I1 and I2.
If a printer is attached to a DS1481, I1 is connected to the printers BUSY signal (low only if printer is on
line and busy), and I2 is connected to SELECT OUT (driven low if printer is off line), see Figure 2.
If the attached printer is “powered up” and on line, the DS1481 uses SELECT OUT for communication
regardless of the state of the printer’s BUSY signal. If the printer is off line its BUSY signal is inactive
(high) and this line is used by the DS1481 for host communication.
If the attached printer is powered off, both SELECT OUT and BUSY will be low. This prevents
meaningful communication with the DS1481 because it is unable to de-assert its busy signal (O1/BSY1
and O2/BSY2 low) or return a high sample of the I/O pin.
To solve this problem, the DS1481 uses the busy signal issued during a reset to detect the presence of
another DS1481 based device attached behind it on the parallel port. If this busy signal is not detected by
the DS1481, it assumes that it is the last DS1481 based device on the port.
If the DS1481 determines that it is the last device on the port it ignores the states of its I1 and I2 pins
while ENI is low. It also leaves the ENO pin high to prevent sending line feed signals to the printer. This
gives the last device the ability to control O1/BSY1 and O2/BSY2 without affecting stackability.
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