Detailed Discription Of #Bm1 Command; Reference Between Signal Data And Screen Display - Hameg Instruments Hm5012-2 Handbuch

Commands from PC to HM5012-2/5014-2
Detailed description of #bm1 command
#BM1(CR) = block mode (transfers 2048 data byte via RS-
232 interface)
The transfer data consist of 2048 byte: trans_byte [0] up to
trans_byte [2047]
The 2048 data byte contain 2001 signal byte, the center
frequency parameter and a check sum for the signal byte.
The signal data allocate the following transfer data byte.
trans_byte[n] = sig_data[n] ( n = 0 bis n = 2000):
trans_byte[0] = sig_data[0]
trans_byte [2000] = sig_data[2000]
The check sum is a 24 bit value ( = 3 Bytes ) and generated as
follows:
Checksum = sig_data[0] +sig_data[1] + ... sig_data[1999] +
sig_data[2000] (sum of all signal data)
The 24 bit check sum allocates the following transfer data
byte:
trans_byte[2044] = 1.Byte of checksum [MSB]
trans_byte[2045] = 2.Byte of checksum
trans_byte[2046] = 3.Byte of check sum [LSB]
The center frequency parameter is allocated to the following
transfer data byte:
trans_byte [2016] = 'C'; trans_byte [2017] = 'F'; trans_byte
[2018] = 'x';
trans_byte [2019] = 'x'; trans_byte [2020] = 'x'; trans_byte [2021]
= 'x';
trans_byte [2022] = '.'; trans_byte [2023] = 'x'; trans_byte [2024]
= 'x';
trans_byte [2025] = 'x'; (x= '0' to '9') Example: CF0623.450
(These bytes are not being used for check sum calculation)
The last sign is always CR ( Carriage Return)
trans_byte[2047] = 0D hex (Carriage Return)
All unused bytes are set to „00 hex".
44
Reference between signal data
and screen display
The signal data are the result of 2001 analog/digital conversions
during one sweep.
X-Position:
The analog value of the first byte „sig_data[0]" is displayed at
the trace start position (left). The following values are displayed
linearly until sig_dat[2000] is reached, which is displayed at the
trace end position (right). The frequency of each signal data
(sample) can be calculated from center frequency and span.
Frequency (x) = (Center Frequency – 0.5 * Span) + Span * x/2000
X = 0... 2000 (Position of sample = sig_data[x])
Y-Position:
The 8 bit value (hex: 00 bis FF) of each memory location for
sig_data[x] has the following relation to the screen:
1C hex (28 dec) coincides with the lowest horizontal graticule
line.
E5 hex (229 dec) coincides with the upmost (reference level)
graticule line.
The a/d converter dependent resolution allows for 25 different Y
positions/div.
In combination with 10dB/div the resolution is 0.4 dB and in case
of 5dB/div it is 0.2dB.
The level (y) of a signal position can be calculated:
For y< 229 (Ref-Level position):
Level in dBm (y) = ref-level (dBm) – ((229-y) * 0.4 dB) at 10dB/
Div
For y > 229 ( Ref-Level position):
Level in dBm (y) = ref-level (dBm) + ((y-229) * 0.4 dB) at 10dB/Div
Subject to change without notice