应用笔记876

Migrating from the MAX7219 and MAX7221 to the MAX6950 and MAX6951 LED Drivers


Abstract: This application note discusses the similarities and differences, both hardware and software, between the older MAX7219 and MAX7221 LED display drivers and the newer MAX6950 and MAX6951 drivers. These drivers are five-digit or eight-digit common-cathode LED display drivers controlled through a high-speed serial interface.

This application note discusses the similarities and differences, both hardware and software, between the older MAX7219 and MAX7221 LED display drivers and the newer MAX6950 and MAX6951 drivers. These drivers are five-digit or eight-digit common-cathode LED display drivers controlled through a high-speed serial interface. Table 1 shows the hardware differences between the drivers.

Table 1. Comparison of Hardware Features
 
MAX7219
MAX7221
MAX6950
MAX6951
Supply voltage minimum
4V
2.7V
Supply voltage maximum
5.5V
5.5V
Maximum segment current
40mA
40mA (V+ = 3.0V)
12mA (2.7V = V+ = 3.0V)
Maximum number of seven-segment digits
8
5
8
Types of seven-segment digits that can be used
Any common-cathode type
Common-cathode types where each digit has independent anode or segment connections
Maximum number of discrete LEDs
64
40
64
Can drive 8x8 matrix digits?
Both packaged and discrete
No
Discrete only
Interface type
4-wire serial
SPI
Interface speed maximum
10Mbits-1
26Mbits-1
Interface Dout pin for cascading devices?
Yes
No
Interface logic input thresholds
Low: 0.8V max, high: 3.5V min
Low: 0.4V max, high: 2.4V min
Through-hole package
24 narrow DIP
 
Surface-mount package
24 wide SO
16 QSOP
Slew-limited LED drive outputs?
Yes
Yes
Multiplex clock generation
Internal fixed
External or internal, 1MHz to 8MHz
Multiplex timing period per digit
150µs
200µs
Automatic segment blinking?
No
Yes
LED intensity levels
16 levels - off, then 1/16 to 15/16 PWM with 1/16 steps
Character decoding
Code B: 0 - 9, -, E, H, L, P, blank
Hexadecimal: 0 - 9, A - F

The newer MAX6950 and MAX6951 drivers are the only choice for systems where 3V or 3.3V is the highest supply voltage available. Their lower logic input thresholds also allow them to be interfaced directly to a microprocessor running from as low as 2.5V. The use of the lowest-possible supply voltage naturally minimizes driver dissipation, making it easier to run the driver at full output current for the brightest display.

The MAX7219 or MAX7221 drivers should be used where the display employed is the "stick" type with the segment connections communed internally. An eight-digit common-cathode stick display would have 8 cathode pins (one for each digit cathode) and 8 segment pins (wired internally to each digit). The MAX6950 and MAX6951 drivers use a multiplexing scheme that changes the segment connections for each digit and cannot be used with internally communed multi-digit types.

Table 2 shows the MAX7219/MAX7221 register set compared with the MAX6950/MAX6951 register set. Although the register functionality is broadly similar, the register addresses are different. However, it is possible to write software code that will interface both register sets correctly. This would allow a processor to write either a MAX7221 or a MAX6951 and achieve the same result. The technique involves selecting a subaddress range for the MAX7221 that does not conflict with the MAX6951 registers. This is shown below as the recommended hex codes. When these MAX7221 registers are written, the appropriate MAX6951 registers are written also, to the addresses in italics. The only problem with this approach is that the MAX6950/MAX6951 control registers (addresses 01 to 07) conflict with the MAX7219/MAX7221 digit registers. The solution is to rewrite the conflicting digit register after every change to the corresponding control register. This seems to be a burden at first, but in practice the control registers are rarely changed after initialization, with the exception of the Intensity register.

Dual-target code will not be able to take advantage of the blink features of the MAX6950/MAX6951 in order to maintain lowest-common-denominator functionality. Also, the decoded font characters above nine are different between the parts.

Table 2. Register Address Map Comparison
MAX7219 AND MAX7221 REGISTERS
HEX CODE
RECOMMENDED HEX CODE
MAX6950 AND MAX6951 REGISTERS
HEX CODE
No-Op
X0
00
No-Op
00
Digit 0
X1
11
 
60
Digit 1
X2
12
 
61
Digit 2
X3
13
 
62
Digit 3
X4
14
 
63
Digit 4
X5
15
 
64
Digit 5
X6
16
 
65
Digit 6
X7
17
 
66
Digit 7
X8
18
 
77
Decode Mode
X9
19
Conflicts with MAX7219/MAX7221 Digit 0
01
Intensity
XA
1A
Conflicts with MAX7219/MAX7221 Digit 1
02
Scan Limit
XB
1B
Conflicts with MAX7219/MAX7221 Digit 2
03
Configuration
XC
1C
Conflicts with MAX7219/MAX7221 Digit 3
04
Display Test
XF
1D
Conflicts with MAX7219/MAX7221 Digit 6
07
 
 
 
Decode Mode
01
 
 
 
Intensity
02
 
 
 
Scan Limit
03
 
 
 
Configuration
04
 
 
 
Display Test
07
 
 
 
Digit 0 plane P0 only (plane 1 unchanged)
20
 
 
 
Digit 1 plane P0 only (plane 1 unchanged)
21
 
 
 
Digit 2 plane P0 only (plane 1 unchanged)
22
 
 
 
Digit 3 plane P0 only (plane 1 unchanged)
23
 
 
 
Digit 4 plane P0 only (plane 1 unchanged)
24
 
 
 
Digit 5 plane P0 only (plane 1 unchanged)
25
 
 
 
Digit 6 plane P0 only (plane 1 unchanged)
26
 
 
 
Digit 7 plane P0 only (plane 1 unchanged)
27
 
 
 
Digit 0 plane P1 only (plane 0 unchanged)
40
 
 
 
Digit 1 plane P1 only (plane 0 unchanged)
41
 
 
 
Digit 2 plane P1 only (plane 0 unchanged)
42
 
 
 
Digit 3 plane P1 only (plane 0 unchanged)
43
 
 
 
Digit 4 plane P1 only (plane 0 unchanged)
44
 
 
 
Digit 5 plane P1 only (plane 0 unchanged)
45
 
 
 
Digit 6 plane P1 only (plane 0 unchanged)
46
 
 
 
Digit 7 plane P1 only (plane 0 unchanged)
47
 
 
 
Digit 0 plane P0 and plane P1 (with same data)
60
 
 
 
Digit 1 plane P0 and plane P1 (with same data)
61
 
 
 
Digit 2 plane P0 and plane P1 (with same data)
62
 
 
 
Digit 3 plane P0 and plane P1 (with same data)
63
 
 
 
Digit 4 plane P0 and plane P1 (with same data)
64
 
 
 
Digit 5 plane P0 and plane P1 (with same data)
65
 
 
 
Digit 6 plane P0 and plane P1 (with same data)
66
 
 
 
Digit 7 plane P0 and plane P1 (with same data)
67



相关型号
MAX6950 串行接口、+2.7V至+5.5V、5位或8位LED显示驱动器 免费样品  
MAX6951 串行接口、+2.7V至+5.5V、5位或8位LED显示驱动器 免费样品  
MAX7219 串行接口、8位、LED显示驱动器 免费样品  
MAX7221 串行接口、8位、LED显示驱动器 免费样品  


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© Jul 17, 2002, Maxim Integrated Products, Inc.
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APP 876: Jul 17, 2002
应用笔记876, AN876, AN 876, APP876, Appnote876, Appnote 876