A Performance Analysis System for the Sport of Bowling

2.7.8 Communication with the COMM Wand
Communications with the module are conducted over a wireless, infrared (IR) interface,
using the TSL251 as the receiver, and two surface-mount LED's as the transmitter. Since
the 87C752 does not contain an on-board hardware UART, a software UART has been
implemented. The software UART conforms to several design constraints specific to the
SMARTDOT module hardware.
Baud Rates: Due to the limited response time of the TSL251, and the relatively
slow conversion rate of the '752's ADC at the module's clock frequency, reliable
reception is only possible up to 600 baud. The communication protocol between the
module and the COMM wand is designed such that the module normally receives
single character transmissions from the wand. Consequently, the 600 baud reception
rate does not create a communications bottle-neck. Since the COMM wand can
receive at a much higher baud rate than the SMARTDOT module, the module
transmits to the COMM wand at up to 38400 baud (another limitation imposed by the
module's clock frequency).
Data Frame: A 12-bit serial protocol is used on transmission: 1 START bit, 8 DATA
bits, 1 PARITY bit (EVEN), and 2 STOP bits. An 11-bit protocol (using a single
STOP bit) is used for reception. This imbalance in STOP bits guarantees a minimal
extra dead space between back-to-back characters, and allows for clock skew between
the module and the COMM wand.
Bit Sampling: The TSL251 and the 87C752's ADC are used for serial reception.
The light waveform is sampled at 4800 Hz (8 samples per bit time), and the middle
four samples of each bit determine the value (0 or 1) for that bit. Ignoring the first
two and last two bit samples allows for some clock skew between the transmit baud
rate of the COMM wand and the receive baud rate of the module. A count of two or
more DARK middle samples constitutes a logical '1', otherwise the bit is considered a
logical '0'. The bias is toward the DARK samples since the COMM wand's presence
over the finger insert creates a dark ambient condition. As long as the COMM wand
is held relatively close to the insert, the background remains dark enough for the
module to discriminate between the light pulses (0's), and the ambient background
level (1's). A noise margin is also built into the bit-sampling scheme. There is a gap
established between the DARK and LITE levels, with the transition point switched
between the two depending on the value of the last sample received, creating a digital
hysteresis function. Refer to Figure A-7 (UART Receive Task Flowchart) and Figure
A-8 (Bit Sample ISR Flowchart).
2.7.9 Communication Protocol
All communications with the module are initiated by pressing on the insert, and then
placing the COMM wand over the insert, covering the opening. The bowler has one
second to remove their finger from the insert, and another second following release to
cover the insert with the COMM wand. If either of these conditions is not met, the
module shuts down and must be reactivated.
Upon activation, the module waits for release to occur, as previously described. When it
identifies a release condition, it looks for a valid waveform. In the case of a COMM
wand transmission, the module discovers that the ball is not rolling within 600 msecs
(through the discrimination and validation routine), switches to the COMM wand
detection routine, and waits for up to one second for the insert to become dark (become
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