
CHAPTER 20
μ
PD78P048A
336
20.3 PROM Programming
The
μ
PD78P048A incorporates a 60-Kbyte PROM as program memory. When programming the
μ
PD78P048A,
the PROM programming mode is set by means of the V
PP
pin and the RESET pin. For the connection of unused
pins, see section
1.5 "Pin Configuration, (2) PROM programming mode
."
Caution
Programs must be written in addresses 0000H to EFFFH. (The last address EFFFH must be
specified.) They cannot be written by a PROM programmer which cannot specify the write
address.
20.3.1 Operating modes
When +5 V or +12.5 V is applied to the V
PP
pin and a low-level signal is applied to the RESET pin, the
μ
PD78P048A is set to the PROM programming mode. This is one of the operating modes shown in Table 20-
4 below according to the setting of the CE, OE, and PGM pins.
The PROM contents can be read by setting the read mode.
Table 20-4. PROM Programming Operating Modes
Pin
RESET
V
PP
V
DD
CE
OE
PGM
D0 to D7
Operating mode
Page data latch
L
+12.5 V
+6.5 V
H
L
H
Data input
Page write
H
H
L
High-impedance
Byte write
L
H
L
Data input
Program verify
L
L
H
Data output
Program inhibit
×
H
H
High-impedance
×
L
L
Read
+5 V
+5 V
L
L
H
Data output
Output disabled
L
H
×
High-impedance
Standby
H
×
×
High-impedance
×
: L or H
(1) Read mode
Read mode is set by setting CE to L and OE to L.
(2) Output disable mode
If OE is set to H, data output becomes high impedance and the output disable mode is set.
Therefore, if multiple
μ
PD78P048As are connected to the data bus, data can be read from any one device
by controlling the OE pin.
(3) Standby mode
Setting CE to H sets the standby mode.
In this mode, data output becomes high impedance irrespective of the status of OE.