MAX6850 MAXIM [Maxim Integrated Products], MAX6850 Datasheet - Page 12

• Manufacturer Part Number: MAX6850
• Description: 4-Wire Interfaced, 7-, 14-, and 16-Segment Alphanumeric Vacuum-Fluorescent Display Controller
• Manufacturer: MAXIM [Maxim Integrated Products]

The user-definable characters are preloaded on power-
up with 24 fonts. These fonts are intended to be useful for
7-segment displays, and include the hexadecimal set for
the first 16 characters, plus eight other useful segment
combinations. Table 12 shows how the 14-segment and
16-segment fonts map to 7-segment displays.
The 48 user-definable font data entries are written and
read through a single register, address 0x05. An
autoincrementing font address pointer in the MAX6850
indirectly accesses the font data. The font address
pointer can be written, setting one of 48 addresses
between 0x00 and 0x2F, but cannot be read back. The
font data is written to and read from the MAX6850 indi-
rectly, using this font address pointer. Unused font
locations can be used as general-purpose scratch
RAM, bearing in mind that the font registers are only 7
bits wide, not 8.
Table 9 shows how to use the single user-defined font
register 0x05 to set the font address pointer, write font
data, and read font data. A read action always returns
font data from the font address pointer position. A write
action sets the 7-bit font address pointer if the MSB is
set, or writes 7-bit font data to the font address pointer
position if the MSB is clear.
The font address pointer autoincrements after a valid
access to the user-definable font data. Autoincrementing
allows the 48-font data entries to be written and read
back very quickly because the font pointer address
needs be set only once. After the last data location 0x2F
has been written, further font data entries are ignored until
the font address pointer is reset. If the font address point-
er is set to an out-of-range address by writing data in the
0xB0 to 0xFF range, then address 0x80 is set instead
(Table 10).
Table 11 shows the user-definable font pointer ad-
dresses.
Table 12 shows bit/segment mapping for user-defined
fonts when applied to 7-, 14-, or 16-segment digits.
4-Wire Interfaced, 7-, 14-, and 16-Segment Alpha-
numeric Vacuum-Fluorescent Display Controller
Table 6. Character Registers Format
12
Writing character data to use font map
data with DP segment unlit
Writing character data to use font map
data with DP segment lit
______________________________________________________________________________________
MODE
0x20 to 0x4F (48/1 mode)
0x20 to 0x7F (96/2 mode)
0x20 to 0x4F (48/1 mode)
0x20 to 0x7F (96/2 mode)
COMMAND ADDRESS
Table 13 illustrates how to set the font address pointer
to a value within the acceptable range. D7 is set (1) to
denote that the user is writing the font address pointer.
If the user attempts to set the font address to one of the
out-of-range addresses by writing data in range 0xB0
to 0xFF, then address 0x00 is set instead.
The font address pointer autoincrements from address
(the last user font location) to point to address 0x00 (the
first user font location). Thus, the font address pointer
autoincrements indefinitely through font RAM.
The cursor register controls the behavior of the cursor
segments (Table 14). The MAX6850 controls 48 cursors
in 48/1 mode, and 96 cursors in 96/2 mode. The cursor
register selects one digit’s cursor to be lit either contin-
uously or blinking. All the other digits’ cursors are off.
The 7 least significant bits (LSBs) of the cursor register
identify the cursor position. The MSB is clear for the
cursor to be on continuously, and set for the cursor to
be lit only during the first half of each blink period.
The valid cursor position address range is contiguous:
0 to 47 (0x00 to 0x2F) for the first row, and 48 to 95
(0x30 to 0x5F) for the 2nd row. If the cursor register is
programmed with an out-of-range value of 95 to 127
(0x60 to 0x7F), then all cursors are off.
The annunciator registers are organized in bytes, with
each segment of each grid being represented by 2
bits. Thus, the four annunciators segments allowed for
each grid are represented by exactly 1 byte (Table 15).
Annunciators are only available in 48/1 mode. The
annunciator address map is shown in Table 4.
The configuration register is used to enter and exit shut-
down, lock the key VFD configuration settings, select
the blink rate, globally clear the digit and annunciator
data, reset the blink timing, and select between 48/1
and 96/2 display modes (Table 16).
D7
0
1
D6
Bits D6 to D0 select font characters 0 to 127
D5
REGISTER DATA
D4
Configuration Register
Annunciator Registers
D3
Cursor Register
D2
D1
D0