NCR 5977-1000, User Manual

Page: 46 / 172

5-34 NCR 5977 2x20 Display Programming
Reset Display
Format
1B 01
Returns
xx yy zz
xx =microcontroller status
00 — OK
If failure occurs, the firmware performs a loop forever.
yy =Flash status
00 — OK, present
01 — Not present
FF — Failure
zz =number (in hexadecimal) of character sets available in the Flash
00=10
Description
This command executes the power–down power–up diagnostic sequence. The
communication lines (RTS for serial, BUSY for parallel) are placed in an exception
condition (see the “Diagnostics” section). The microcontroller test consists of a sum–
check test on the ROM and a write/read test on the RAM. A check–sum test is also
performed on the FLASH that holds any user defined character sets. After executing the
command, the three status bytes (see above) are sent to the host, the display screen is
cleared, the cursor moves to the 0 position, communication line exception conditions
are cleared, and all registers and variables are initialized. Note that the screen is cleared
during this command. If a host needs previous data redisplayed, the host must resend
the previous data after this command has completed. Since true bi–directional
communications are not available for the parallel interface, a unique interface utilizing
the Strobe line as a clock line and the Ack line as a data line is used.