Application
Consequently, writing RAM register values to EEPROM is enabled but generates a warning message on
the evaluation module. The GUI allows the user to store their own register configurations on the PC as
.reg files as an alternative to programming the EEPROM. These configuration files can then be restored
manually as desired, such as after a power cycle. Alternatively, new configurations for the bq76PL455A-
Q1 are written to RAM directly after any new power cycle using the controls in the GUI.
4.6
Communications
Communication between the PC GUI and the first bq76PL455EVM is done via a USB-to-TTL Serial
converter cable. This cable connects to the J3 - Serial connector on the bq76PL455EVM. Communication
between all subsequent stacked bq76PL455EVMs is done over isolated, differential twisted pair, daisy
chained communication lines connected between the J4 - Diff Comm Low and J5 - Diff Comm High
connectors of neighboring bq76PL455EVMs. The communication rate between the PC and the first of
potentially multiple stacked modules is adjustable to various baud rates from 125K to 1M, whereas the
communication rate over the daisy chain link is fixed. The typical minimum bit period over the daisy chain
link is 125 ns (8 MHz). Communication over the differential daisy chain link is transparent to the user via
the GUI, as the conversion between the single-ended communications link and the differential
communications link is handled in hardware by the bq76PL455A-Q1.
Communication is mastered by the PC GUI using a command and response protocol which allows the
GUI to configure and read back data from slave bq76PL455EVMs. Under the command and response
protocol, communication with the bq76PL455EVM(s) is always initiated by the GUI which issues a
command frame. Command frames are addressed to either an individual bq76PL455A-Q1, sent as a
broadcast to a pre-specified group of consecutively addressed bq76PL455A-Q1 devices, or sent as a
general broadcast to all bq76PL455A-Q1 devices on the J4 - Diff Comm Low and J5 - Diff Comm High
bus. Some command types are currently supported by the GUI only in the
Extended Window
interface.
The following six types of command frames are supported by the bq76PL455A-Q1:
1. Write to a single bq76PL455A-Q1 causing a returned response (that is, essentially a “read” command).
2. Write to a single bq76PL455A-Q1 with no response.
3. Write to a pre-defined group of bq76PL455A-Q1 devices to generate a series of responses (device
with highest address in group responds first).
4. Write to a pre-defined group of bq76PL455A-Q1 devices without a response request.
5. Write to all connected bq76PL455A-Q1 devices to generate a series of responses (device with the
highest address responds first).
6. Write to all connected bq76PL455A-Q1 devices with no responses generated.
The GUI currently uses command types 1, 2 and 6 from the aforementioned list during its operation as
part of the graphical interface. The remaining command frame types are accessible only through the
extended window manual command interface and scripting options.
On the bq76PL455EVM, high-voltage isolation is provided on all of the twisted pair differential
communication links between each stacked evaluation module.
The serial bus allows Command frames to be transmitted by the PC and to be received by all
bq76PL455EVMs. Response frames, when requested, are transmitted by any addressed bq76PL455EVM
back to the PC.
Since response frames are only ever sent in response to command frames, a single physical pair of wires
is used to communicate between any two neighboring bq76PL455A-Q1 devices in a half duplex manner to
alternately send and receive data. The physical differential pair connections are implemented using
capacitive-coupling and are designed to meet the needs of wired differential communications in
automotive applications.
For battery systems with more than 16 cells where multiple bq76PL455EVMs are stacked, each evaluation
module must have a unique address. Although the bq76PL455A-Q1 IC allows addresses to be set either
with the GPIO lines in hardware or via software, the evaluation module and GUI are, by default, auto-
addressed by the GUI when the GUI starts. If more than one evaluation module is connected,
bq76PL455EVMs are auto-addressed with addresses from 0 to n – 1, where n is the number of modules
connected. The bq76PL455EVM connected to the PC is address 0, the first daisy-chained evaluation
module is at address 1, the second daisy-chained evaluation module is at address 2, and so on.
8
bq76PL455EVM and GUI User Guide
SLUUBA7A – April 2015 – Revised July 2015
Copyright © 2015, Texas Instruments Incorporated
