RCA RMB-167 - Manual (Page 26)

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7.2 Analog-to-Digital Converter Reference Jumpers
The analog-to-digital converter requires a ground and reference voltage. These reference
voltages may be provided either from JP2 lines marked VG (ground reference voltage) and VR
(reference voltage), or connected to the +5 volt TTL supply. Jumpers JP4 and JP5 select the
source of reference voltages. The center posts of JP4 and JP5 are connected to the SAB-C167
VAREF and VAGND inputs. Post 1 of JP4, marked VCC is connected to the +5 volt supply.
Thus, connecting this post with the center post selects VAREF to be the same as the +5 volt
supply. In the alternate position, VAREF is to be supplied from JP7 from the terminal marked VR.
Similarly, the post marked GND of JP5 is connected to the ground of the supply. Connecting the
center post of JP5 with the post marked GND selects VAGND to be the same as the ground of
the supply voltage. In the alternate position, the ground reference is to be supplied from the JP7
terminal marked VG.