== Usage in CPCs ==
=== Aleste 520EX ===
Used by [[Aleste 520EX]] (a CPC clone with built-in RS232 interface):
EEXXh Aleste - 8251 USART chip (RS232/Mouse) Data (R/W)
EFXXh Aleste - 8251 USART chip (RS232/Mouse) Control/Status (R/W)
Uses a KR580WW51A (russian clone of the 8251).
Clock source comes from a [[8253 chip]].
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=== MHT Ingenieros RS232 para Amstrad ===
Used by RS-232 para Amstrad from MHT Ingenieros, mapped to Ports:
FADCh - MHT RS232 - 8251 USART data
FADDh - MHT RS232 - 8251 USART control/status
Clock source comes from a [[8253 chip]].
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=== Cirkir Serial Interface ===
Used by [[Cirkit serial interface]] (for use with the included Prestel Link modem)):
FADFh - Cirkit - 8251 UART Data register
FBDFh - Cirkit - 8251 UART Status/Control register
TX clock source is fixed (19.2KHz), RX clock source can be selected via DTR bit (1200Hz or 19.2KHz).
== Registers ==
Bit Expl.
0-7 Data
== Usage in CPCs ==
=== Aleste 520EX ===
Used by [[Aleste 520EX]] (a CPC clone with built-in RS232 interface):
EEXXh Aleste - 8251 USART chip (RS232/Mouse) Data (R/W)
EFXXh Aleste - 8251 USART chip (RS232/Mouse) Control/Status (R/W)
Uses a KR580WW51A (russian clone of the 8251).
Clock source comes from a [[8253 chip]].
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=== MHT Ingenieros RS232 para Amstrad ===
Used by [[RS-232 para Amstrad]] from MHT Ingenieros, mapped to Ports:
FADCh - MHT RS232 - 8251 USART data
FADDh - MHT RS232 - 8251 USART control/status
Clock source comes from a [[8253 chip]].
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=== Schneiderware V/24 Interface ===
Used by [[Schneiderware V/24 Interface]] from [[CPC Schneider International]], mapped to Ports:
F9E0h (or F9E2h) Schneiderware V/24 8251 USART chip Data
F9E1h (or F9E3h) Schneiderware V/24 8251 USART chip Control
Clock source comes from a [[8253 chip]].
Clock input to that chip is jumper-selectable: 2MHz (default), or 1MHz.
Caution: The RTS/CTS and DSR/DTR handshaking signals are disabled by
default (via jumpers) (and, in worst case, also by additional inaccesible
hardwired connections, hidden underneath of the jumpers)
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=== Cirkit Serial Interface ===
Used by [[Cirkit serial interface]] (for use with the included Prestel Link modem)):
FADFh - Cirkit - 8251 UART Data register
FBDFh - Cirkit - 8251 UART Status/Control register
TX clock source is fixed (19.2KHz), RX clock source can be selected via DTR bit (1200Hz or 19.2KHz).
== 8251 vs 8251A ==
The original '''8251''' seems to be very rare (there's no programming info found in the internet). The '''8251A''' is backwards compatible, but includes some additional features. The 8251A gives some details on the additional features, so one could eventually use the '''8251A''' datasheet to reconstruct the functionality of the original '''8251'''.
However, since the 8251 is so rare, it's rather doubtworthy doubtful that the Aleste or Circit actually uses that these chips, they probably they use 8251A chips.
* The Circit advert says 8251 (which is maybe meant to be an abbreviation for 8251A).
* [[Media:8251A.pdf]] - newer 8251A datasheet (detailed info)
* [[Media:8251.pdf]] - older 8251 datasheet (pin-outs out only, without programming info) [[Category:Electronic Component]]