Hospira LifeCare XL Series, Technical & Service Manual

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4.2 ELECTRONICS OVERVIEW
Technical Service Manual 4 - 7 430-00587-008 (Rev. 2/05)
The LOCHG_REQ signal alerts the MCU PWA of the battery voltage level; it is generated
by U6A, U7B, U7C, U7D and associated passive components.
IC U6A, resistors R24 through R28, and capacitor C20 constitute a differential amplifier
that reads the battery voltage as it is being charged. The output of the differential amplifier
is compared to a previously determined level by U7C. U7C generates the LOCHG_REQ.
The voltage level depends on whether U7-13 or U7-1 is low or, alternatively, whether
battery type 1 or battery type 2 is connected.
4.2.3
MCU PWA
The MCU PWA contains micro controller U6 (see Figure 9-15, MCU PWA Schematic (XL) ,
Figure 9-16, MCU PWA Schematic (XLM) , or Figure 9-17, MCU PWA Schematic
(XLM with DataPort)) . The MCU PWA has five digital ports and one analog port. Each port
is eight lines wide. The MCU PWA also includes the following circuitry:
❏
Watchdog
❏
Serial communication
❏
Alarm
❏
Alarm power backup
❏
Motor drivers
❏
Pin detector
❏
Universal asynchronous receiver/transmitter (UART) (XLM with DataPort)
4.2.3.1
WATCHDOG CIRCUITRY
The watchdog circuitry continuously monitors the MCU PWA and contains IC U14. U14
is strobed by micro controller U16 at a predetermined minimum frequency; otherwise, the
*RESET output becomes active. *RESET also becomes active if digital voltage (VDIG) is
out of range. *RESET causes the MCU PWA to reset, blocks any signal to the motors, and
turns the alarm on.
4.2.3.2
SERIAL COMMUNICATION CIRCUITRY
The serial communication circuitry interchanges data between the MCU PWA and either
the liquid crystal display (LCD) screen or the electrically erasable programmable read-only
memory (EEPROM).
Although data is transmitted to both the LCD screen and the EEPROM, the clock is diverted
only to the selected receiver. If EE_CS is active, then *SCK appears as EE_CLK at IC U9C.
If EE_CS is inactive, then *SCK is inverted to appear as LCD_CLK at IC U8B.
Data is read from either the LCD screen or the EEPROM. If EE_CS is active, then EE_DO
appears as RXD at IC U7C. If EE_CS is inactive, then LCD_DO is inverted to appear as
RXD at IC U7C.