comparison: content/hp34970a_3.rst
content/hp34970a_3.rst
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| 7 :Tags: HP, 34970A, DMM, repair, test equipment | 7 :Tags: HP, 34970A, DMM, repair, test equipment |
| 8 :series: HP 34970A repair | 8 :series: HP 34970A repair |
| 9 :series_index: 3 | 9 :series_index: 3 |
| 10 | 10 |
| 11 | 11 |
| 12 As explained in `the previous post in this series <{filename}/hp34970a_2.rst>`_, I've started to sniff the serial | 12 As explained in `the previous post in this series <{filename}/hp34970a_2.rst>`_, |
| 13 protocol between the main board and the display panel so I can replace | 13 I've started to sniff the serial protocol between the main board and |
| 14 the failed VFD by an OLED or TFT display managed by an arduino or | 14 the display panel so I can replace the failed VFD by an OLED or TFT |
| 15 similar. | 15 display managed by an arduino or similar. |
| 16 | 16 |
| 17 Protocol | 17 Protocol |
| 18 ======== | 18 ======== |
| 19 | 19 |
| 20 The serial communication takes place at a rather unusual speed: 187.5 | 20 The serial communication takes place at a rather unusual speed: 187.5 |
| 42 themselves. | 42 themselves. |
| 43 | 43 |
| 44 - ``<0x55>``: end of transmission. | 44 - ``<0x55>``: end of transmission. |
| 45 | 45 |
| 46 | 46 |
| 47 I've only identified 2 commands for now, but these are the most | 47 I've only identified 3 commands for now, but these are the most |
| 48 important ones: | 48 important ones: |
| 49 | 49 |
| 50 - ``0x00``: send the chars to the main display | 50 - ``0x00``: send the chars to the main display |
| 51 - ``0x0C``: send the chars to the secondary channel display | 51 - ``0x0C``: send the chars to the secondary channel display |
| 52 - ``0x0A``: set the display indicators | |
| 52 | 53 |
| 54 | |
| 55 Main display | |
| 56 ------------ | |
| 57 | |
| 58 Characters are simply sent to the display. However, to specify that a | |
| 59 part of the string to display should be less bright (usually, the | |
| 60 selected option is bright and the other ones are dim), the CPU insert | |
| 61 a special character (need to check which hexadecimal value it is) at | |
| 62 the beginning and the end of the dim part of the string. | |
| 63 | |
| 64 | |
| 65 Channel display | |
| 66 --------------- | |
| 67 | |
| 68 Seems there is nothing special there. The frame payload always consist | |
| 69 in 3 characters (the 3 digits). | |
| 70 | |
| 71 | |
| 72 Indicator flags | |
| 73 --------------- | |
| 74 | |
| 75 The indicator flags are always sent as 4 bytes, each bit controlling | |
| 76 one indicator. | |
| 77 | |
| 78 The indicator flags I've been able to identify so far | |
| 79 are below. | |
| 80 | |
| 81 Let's say the frame is: ``<0x0A> <0x04> <F1> <F2> <F3> <F4>``, then: | |
| 82 | |
| 83 | |
| 84 - F1.7 = | |
| 85 - F1.6 = | |
| 86 - F1.5 = | |
| 87 - F1.4 = | |
| 88 - F1.3 = | |
| 89 - F1.2 = Mx+B enabled | |
| 90 - F1.1 = Alarm enabled (or the alarm frame) | |
| 91 | |
| 92 - F2.5 = 4W | |
| 93 - F2.4 = | |
| 94 - F2.1 = | |
| 95 | |
| 96 - F3.6 = | |
| 97 - F3.5 = | |
| 98 | |
| 99 - F4.7 = CONFIG (not sure) | |
| 100 - F4.6 = | |
| 101 - F4.5 = MON | |
| 102 - F4.4 = VIEW | |
| 103 - F4.3 = | |
| 104 - F4.2 = | |
| 105 - F4.1 = | |
| 106 | |
| 107 | |
| 53 | 108 |
| 54 Quick prototype | 109 Quick prototype |
| 55 =============== | 110 =============== |
| 56 | 111 |
| 57 With this very incomplete reverse ingeeniring of the communication, I | 112 With this very incomplete reverse ingeeniring of the communication, I |
