Test-Ok eC-test-mate, Hardware Reference Manual

Page: 11 / 35

Copyright © TEST-OK. All Rights Reserved.
11 / 35
Serial Channel (UART 101)
The serial channel is designed to work with signal levels up to 5V. The actual output voltage is equal to the
voltage that is configured for Digital Output Group 101 if this voltage is equal or less than 5V. For higher
Group 101 voltages, the Serial channel is fixed at 5V.
The Serial input has a fixed VIHmin of 1.7V.
The SERAL_TX pin is driven by a level shifter (SN74LVC1T45) with a series resistor of 100 Ω. This means
that the sink and source current of the output is limited.
The baud rate, parity and some other parameters can be configured via a configuration command.
Two buffers are associated with the serial channel, one for transmission and one for reception. Transmission
is initiated by sending one or more bytes to the TEST-OK Board by means of the SERIAL_TX command.
The bytes in this packet are copied to the transmit buffer and then sent over the serial interface using the
configured baud rate and parity.
Received bytes are stored in the receive buffer. These bytes can be sent to the host in two ways: either on
request of the host ('polling' mode) or when one of two configured conditions occur ('interrupt' mode): more
than <n> bytes are present in the buffer (RxThreshold) or one or more bytes are present in the buffer and no
new data is received for more than <t> milliseconds (RxTimeout).
When StxMode is enabled (see description below), then the reception of an ETX byte will also result in the
buffer contents being sent to the PC.
The interrupt method is best and guarantees that there is no unnecessary delay between the reception of
data and the availability on the host.
The RxTimeout method allows to synchronize with the stream of bytes from the target board when there is
some time between two consecutive packets.
Note 1: the naming of the connector pins is as seen from the eC-test-mate. SERIAL_TX is therefore an
output on which the data towards the UUT is provided by the EC-test-mate and SERIAL_RX is an input on
which data from the UUT is received.
Note 2: the output (transmit) driver on the eC-test-mate Type I has a 100R series resistor and may therefore
not be able to source or sink excessive loads on the UUT. For higher baud rates, this may also have an
impact on the wave forms.
Configurable parameters and their default after start-up or reset:
Parameter Description Default
Value
Baud rate Baud rate of the serial channel. See the table below for information on the
error % for standard baud rates.
Non-standard baud rates are supported as well as long as they are in the
range 300..11520 baud. 9600 baud
Parity Determines whether a parity bit is sent and whether it is even or odd No parity
RxInterrupt If 'on', the TEST-OK Board will send RX_RECEIVE packets without waiting for
a host request Off
RxThreshold Number of received bytes in the Rx buffer that will generate an 'interrupt' 32 bytes
RxTimeout Time after which received bytes are sent to the host in the absence of new
data 100 ms
StxMode If set, the TEST-OK firmware will put STX and ETX bytes around the packet
and DLE's will be inserted if necessary. off
Some standard Baud Rates and their error percentage:
Baud Rate Actual Rate % Error
300 300 0.00
1200 1200 0.00
2400 2400 0.02
9600 9606 0.06
19200 19193 -0.03