Oki ML420 Maintenance Manual page 11

(2) Program ROM
This is a 256 × 16 bits (4M bit) EPROM or MASK ROMwith the control program for the
printer stored. The MPU executes instructions under this program.
The program ROM is assigned to the program memory area of the MPU and is fetched
by the PSEN-N signal of the MPU.
The following shows the operation of the memory access.
42113901TH01 Rev.3
MPU
A0~A17
D0~D15
CSO
PSEN
MPU CLOCK
A0~A17
PG-N
PSEN-N
D0~D15
ROM
PG-N
CE
PSEN-N
OE
Oki Data CONFIDENTIAL
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