LED

Digit

6*

SEG dp

SEG g

SEG f

SEG e

SEG d

SEG c

CC6

SEG b

SEG

a

LED

Digit

7*

SEG dp

SEG g

SEG f

SEG e

SEG d

SEG c

SEG b

CC7

SEG

a

*These digits are not available for the MAX6950.

The MAX6950 and MAX6951 were intended to drive single-digit displays, and this allows the segments

for each digit to be routed to the correct driver pin. Many dual-digit displays pin out the two digits

separately, treating the digits as two singles in one package. These can be driven directly by the

MAX6950 and MAX6951. Other dual-digit displays internally pair the segment anodes for the two digits

(Figure 1) and these displays present issues.

The problem can be understood by checking the SEG dp entries in Table 1 for Digit 0 and Digit 1. SEG

dp is connected to a different pin for each digit. However, a multiplex dual-digit display commons these

connections internally (Figure 1), effectively shorting Pin 5 and Pin 6 of the driver.

Figure 1. Internal connections for a multiplex dual-digit display

Two simple solutions are presented here.

The first solution simply sacrifices the segment drive that share a cathode drive for each dual-digit. This

is SEG dp for Digit 0 and Digit 1 discussed earlier. By examining Table 1, it can be seen that the other

sacrificed segments are SEG f for Digit 2 and Digit 3, SEG d for Digit 4 and Digit 5, and SEG b for Digit

6 and Digit 7. However, it's usually the DP segments that applications can sacrifice, not segments

within the seven-segment digit.

If the DPs are not required, then the connections shown in Table 2 can be used. This is a rework of the

standard connections shown in Table 1, with the segments moved so that all segments apart from the

DP segments are available. The DP segment connections on the displays are simply left unused. The

no-decode operation should not be selected when this (or any other nonstandard) pin mapping is used.

The MAX6950 or MAX6951's internal hexadecimal fonts display correctly in decode mode only when

the standard display connections are being used.