Circuit Description - Sharp ER-04RP Service Manual

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5. Circuit description
5-1. General
The ER-04RP is a remote printer using the SRN
work) as an external interface through which
electronic cash register and a POS tefiinal.
(Sharp Retail Net-
connected to an
The remote printe; has a control circuit that consists mainly of a CPU,
a ROM, a RAM, and their peripheral circuits, an SRN interface circuit
for interfacing with the host, an operation panel circuit for operation
switch inputs and LED display, an auto cutter circuit a printer
mechanism, and a power supply circuit for supplying necessaw
power to each circuit.
Fig.5-l shows a block diagram of the remote printer.
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5-2. SRN control circuit
1) UOallocation and memory mapping
The
CPU used in the SRN control circuit is a single chip 8-bit C-MOS
microprocessor with an external memory.
In addition to general purpose 1/0 ports, the CPU has expansion 1/0
ports externally allocated on the memory space.
It has an address space of 64K bytes, with a ROM, a RAM, and
external expansion 1/0s peripherally arranged as shown in the at-
tached page.
The RAM has a capacity of 64K bits or 256K bits according to the
destination, the RAM size being checked by software.
Data and control commands are transferred to and from the SRN
through the registers in the SRN interface circuit which are ailocated
on the memory space.
The ROM has a capacity of 256K bits and contains control software
and CG data for character printouts.
2) CPU peripheral circuitry
The M50734SP CPU is a CPU with an external memory, and reads
the 8 low-order bits of the address through the AO/DObus lines from
an 8-bit latch HC373.
The ROM has a capacity of 256K bits, and the RAM 64K bits or 256K
bits. A super capacitor is used to provide backup power in case of a
power failure.
IC9 (74HCOO) is also operated on the VRAM power supply for
standby control.
A ceramic oscillator is used as the CPU clock to provide a clock
frequency of 7.37MH2.
Fig,5-1 ER-03RP block diagram
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Fig.5-2 ROM/RAM circuits
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