C515A_9708 Datasheet, PDF (38/182 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

External Bus Interface
C515A
4.4 ALE, Address Latch Enable
The C515A allows to switch off the ALE output signal. If the internal ROM is used (EA=1 and PC ≤
7FFFH) and ALE is switched off by EALE=0, then, ALE will only go active during external data
memory accesses (MOVX instructions). If EA=0, the ALE generation is always enabled and the bit
EALE has no effect.
After a hardware reset the ALE generation is enabled.
Special Function Register SYSCON (Address B1H)
Reset Value : XX10XX01B
Bit No. MSB
7
B1H
–
6
5
4
3
– EALE RMAP –
LSB
2
1
0
– XMAP1 XMAP0 SYSCON
The function of the shaded bits are not described in this section.
Bit
EALE
–
Function
Enable ALE output
EALE = 0 : ALE generation is disabled; disables ALE signal generation
during internal code memory accesses (EA=1). With EA=1,
ALE is automatically generated at MOVX instructions.
EALE = 1 : ALE generation is enabled
If EA=0, the ALE generation is always enabled and the bit EALE has no
effect on the ALE generation.
Reserved bits for future use. Read by CPU returns undefined values.
Semiconductor Group
4-4
1997-08-01