The 6551 ACIA is an RS232 serial controller. It is used in the RF57-232 expansion for Thomson computers, allowing use as a standard RS232 serial port, or an RS-232-like serial link at TTL levels, to communicate with a Minitel.
The ACIA has only 4 registers, making it relatively easy to work with.
This register is used to read received data bytes, and write outgoing ones.
this register is read-only.
Bit | Description | Cleared by | Hardware reset value | Software reset value |
---|---|---|---|---|
0 | Parity error | Self-clearing | 0 | - |
1 | Framing error | Self-clearing | 0 | - |
2 | Overrun | Self-clearing | 0 | 0 |
3 | Receive data register full | Reading data register | 0 | - |
4 | Transmit data register empty | Writing data register | 1 | - |
5 | /DCD | Reflects /DCD pin state | - | - |
6 | /DSR | Reflects /DSR pin state | - | - |
7 | IRQ | Reading status register | 0 | - |
The “self-clearing” status bits are cleared after reading the data register, and successfully receiving one byte.
Bits 7-5: parity check configuration
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Bits 4-2: transmitter control
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Controls the /DTR pin and enables the receiver.
When set to 0, always use 1 stop bit. When set to 1: