// license:BSD-3-Clause
// copyright-holders:smf
/*********************************************************************
i8251.c
Intel 8251 Universal Synchronous/Asynchronous Receiver Transmitter code
NEC uPD71051 is a clone
The V53/V53A use a customized version with only the Asynchronous mode
and a split command / mode register
*********************************************************************/
#include "emu.h"
#include "i8251.h"
//#define VERBOSE 1
#include "logmacro.h"
//**************************************************************************
// DEVICE DEFINITIONS
//**************************************************************************
DEFINE_DEVICE_TYPE(I8251, i8251_device, "i8251", "Intel 8251 USART")
DEFINE_DEVICE_TYPE(V53_SCU, v53_scu_device, "v63_scu", "NEC V53 SCU")
//-------------------------------------------------
// i8251_device - constructor
//-------------------------------------------------
i8251_device::i8251_device(
const machine_config &mconfig,
device_type type,
const char *tag,
device_t *owner,
uint32_t clock)
: device_t(mconfig, type, tag, owner, clock),
device_serial_interface(mconfig, *this),
m_txd_handler(*this),
m_dtr_handler(*this),
m_rts_handler(*this),
m_rxrdy_handler(*this),
m_txrdy_handler(*this),
m_txempty_handler(*this),
m_syndet_handler(*this),
m_cts(1),
m_dsr(1),
m_rxd(0),
m_rxc(0),
m_txc(0)
{
}
i8251_device::i8251_device(const machine_config &mconfig, const char *tag, device_t *owner, uint32_t clock)
: i8251_device(mconfig, I8251, tag, owner, clock)
{
}
v53_scu_device::v53_scu_device(const machine_config &mconfig, const char *tag, device_t *owner, uint32_t clock)
: i8251_device(mconfig, V53_SCU, tag, owner, clock)
{
}
//-------------------------------------------------
// device_start - device-specific startup
//-------------------------------------------------
void i8251_device::device_start()
{
// resolve callbacks
m_txd_handler.resolve_safe();
m_rts_handler.resolve_safe();
m_dtr_handler.resolve_safe();
m_rxrdy_handler.resolve_safe();
m_txrdy_handler.resolve_safe();
m_txempty_handler.resolve_safe();
save_item(NAME(m_flags));
save_item(NAME(m_sync_byte_offset));
save_item(NAME(m_sync_byte_count));
save_item(NAME(m_sync_bytes));
save_item(NAME(m_status));
save_item(NAME(m_command));
save_item(NAME(m_mode_byte));
save_item(NAME(m_cts));
save_item(NAME(m_dsr));
save_item(NAME(m_rxd));
save_item(NAME(m_rxc));
save_item(NAME(m_txc));
save_item(NAME(m_rxc_count));
save_item(NAME(m_txc_count));
save_item(NAME(m_br_factor));
save_item(NAME(m_rx_data));
save_item(NAME(m_tx_data));
}
/*-------------------------------------------------
update_rx_ready
-------------------------------------------------*/
void i8251_device::update_rx_ready()
{
int state = m_status & I8251_STATUS_RX_READY;
// masked?
if (!BIT(m_command, 2))
state = 0;
m_rxrdy_handler(state != 0);
}
/*-------------------------------------------------
receive_clock
-------------------------------------------------*/
void i8251_device::receive_clock()
{
/* receive enable? */
if (BIT(m_command, 2))
{
const bool sync = is_receive_register_synchronized();
if (sync)
{
--m_rxc_count;
if (m_rxc_count)
return;
}
//logerror("I8251\n");
/* get bit received from other side and update receive register */
receive_register_update_bit(m_rxd);
if (is_receive_register_synchronized())
m_rxc_count = sync ? m_br_factor : (3 * m_br_factor / 2);
if (is_receive_register_full())
{
receive_register_extract();
receive_character(get_received_char());
}
}
}
/*-------------------------------------------------
is_tx_enabled
-------------------------------------------------*/
bool i8251_device::is_tx_enabled() const
{
return BIT(m_command , 0) && !m_cts;
}
/*-------------------------------------------------
check_for_tx_start
-------------------------------------------------*/
void i8251_device::check_for_tx_start()
{
if (is_tx_enabled() && (m_status & (I8251_STATUS_TX_EMPTY | I8251_STATUS_TX_READY)) == I8251_STATUS_TX_EMPTY)
start_tx();
}
/*-------------------------------------------------
start_tx
-------------------------------------------------*/
void i8251_device::start_tx()
{
LOG("start_tx %02x\n", m_tx_data);
transmit_register_setup(m_tx_data);
m_status &= ~I8251_STATUS_TX_EMPTY;
m_status |= I8251_STATUS_TX_READY;
}
/*-------------------------------------------------
transmit_clock
-------------------------------------------------*/
void i8251_device::transmit_clock()
{
m_txc_count++;
if (m_txc_count != m_br_factor)
return;
m_txc_count = 0;
if (is_transmit_register_empty())
{
if ((m_status & I8251_STATUS_TX_READY) == 0 && (is_tx_enabled() || (m_flags & I8251_DELAYED_TX_EN) != 0))
start_tx();
else
m_status |= I8251_STATUS_TX_EMPTY;
update_tx_ready();
update_tx_empty();
}
/* if diserial has bits to send, make them so */
if (!is_transmit_register_empty())
{
uint8_t data = transmit_register_get_data_bit();
m_txd_handler(data);
}
#if 0
/* hunt mode? */
/* after each bit has been shifted in, it is compared against the current sync byte */
if (BIT(m_command, 7))
{
/* data matches sync byte? */
if (m_data == m_sync_bytes[m_sync_byte_offset])
{
/* sync byte matches */
/* update for next sync byte? */
m_sync_byte_offset++;
/* do all sync bytes match? */
if (m_sync_byte_offset == m_sync_byte_count)
{
/* ent hunt mode */
m_command &= ~(1<<7);
}
}
else
{
/* if there is no match, reset */
m_sync_byte_offset = 0;
}
}
#endif
}
/*-------------------------------------------------
update_tx_ready
-------------------------------------------------*/
void i8251_device::update_tx_ready()
{
/* clear tx ready state */
int tx_ready;
/* tx ready output is set if:
DB Buffer Empty &
CTS is set &
Transmit enable is 1
*/
tx_ready = is_tx_enabled() && (m_status & I8251_STATUS_TX_READY) != 0;
m_txrdy_handler(tx_ready);
}
/*-------------------------------------------------
update_tx_empty
-------------------------------------------------*/
void i8251_device::update_tx_empty()
{
if (m_status & I8251_STATUS_TX_EMPTY)
{
/* tx is in marking state (high) when tx empty! */
m_txd_handler(1);
}
m_txempty_handler((m_status & I8251_STATUS_TX_EMPTY) != 0);
}
//-------------------------------------------------
// device_reset - device-specific reset
//-------------------------------------------------
void i8251_device::device_reset()
{
LOG("I8251: Reset\n");
/* what is the default setup when the 8251 has been reset??? */
/* i8251 datasheet explains the state of tx pin at reset */
/* tx is set to 1 */
m_txd_handler(1);
/* assumption */
m_rts_handler(1);
m_dtr_handler(1);
transmit_register_reset();
receive_register_reset();
m_flags = 0;
/* expecting mode byte */
m_flags |= I8251_EXPECTING_MODE;
/* not expecting a sync byte */
m_flags &= ~I8251_EXPECTING_SYNC_BYTE;
/* no character to read by cpu */
/* transmitter is ready and is empty */
m_status = I8251_STATUS_TX_EMPTY | I8251_STATUS_TX_READY;
m_mode_byte = 0;
m_command = 0;
m_rx_data = 0;
m_tx_data = 0;
m_rxc_count = m_txc_count = 0;
m_br_factor = 1;
/* update tx empty pin output */
update_tx_empty();
/* update rx ready pin output */
update_rx_ready();
/* update tx ready pin output */
update_tx_ready();
}
/*-------------------------------------------------
control_w
-------------------------------------------------*/
void i8251_device::command_w(uint8_t data)
{
/* command */
LOG("I8251: Command byte\n");
m_command = data;
LOG("Command byte: %02x\n", data);
if (BIT(data, 7))
LOG("hunt mode\n");
if (BIT(data, 5))
LOG("/rts set to 0\n");
else
LOG("/rts set to 1\n");
if (BIT(data, 2))
LOG("receive enable\n");
else
LOG("receive disable\n");
if (BIT(data, 1))
LOG("/dtr set to 0\n");
else
LOG("/dtr set to 1\n");
if (BIT(data, 0))
LOG("transmit enable\n");
else
LOG("transmit disable\n");
/* bit 7:
0 = normal operation
1 = hunt mode
bit 6:
0 = normal operation
1 = internal reset
bit 5:
0 = /RTS set to 1
1 = /RTS set to 0
bit 4:
0 = normal operation
1 = reset error flag
bit 3:
0 = normal operation
1 = send break character
bit 2:
0 = receive disable
1 = receive enable
bit 1:
0 = /DTR set to 1
1 = /DTR set to 0
bit 0:
0 = transmit disable
1 = transmit enable
*/
m_rts_handler(!BIT(data, 5));
m_dtr_handler(!BIT(data, 1));
if (BIT(data, 4))
m_status &= ~(I8251_STATUS_PARITY_ERROR | I8251_STATUS_OVERRUN_ERROR | I8251_STATUS_FRAMING_ERROR);
if (BIT(data, 6))
{
// datasheet says "returns to mode format", not
// completely resets the chip. behavior of DEC Rainbow
// backs this up.
m_flags |= I8251_EXPECTING_MODE;
}
check_for_tx_start();
update_rx_ready();
update_tx_ready();
update_tx_empty();
}
void i8251_device::mode_w(uint8_t data)
{
LOG("I8251: Mode byte = %X\n", data);
m_mode_byte = data;
/* Synchronous or Asynchronous? */
if ((data & 0x03) != 0)
{
/* Asynchronous
bit 7,6: stop bit length
0 = inhibit
1 = 1 bit
2 = 1.5 bits
3 = 2 bits
bit 5: parity type
0 = parity odd
1 = parity even
bit 4: parity test enable
0 = disable
1 = enable
bit 3,2: character length
0 = 5 bits
1 = 6 bits
2 = 7 bits
3 = 8 bits
bit 1,0: baud rate factor
0 = defines command byte for synchronous or asynchronous
1 = x1
2 = x16
3 = x64
*/
LOG("I8251: Asynchronous operation\n");
const int data_bits_count = ((data >> 2) & 0x03) + 5;
LOG("Character length: %d\n", data_bits_count);
parity_t parity;
if (BIT(data, 4))
{
if (BIT(data, 5))
{
LOG("enable parity checking (even parity)\n");
parity = PARITY_EVEN;
}
else
{
LOG("enable parity checking (odd parity)\n");
parity = PARITY_ODD;
}
}
else
{
LOG("parity check disabled\n");
parity = PARITY_NONE;
}
stop_bits_t stop_bits;
switch ((data >> 6) & 0x03)
{
case 0:
default:
stop_bits = STOP_BITS_0;
LOG("stop bit: inhibit\n");
break;
case 1:
stop_bits = STOP_BITS_1;
LOG("stop bit: 1 bit\n");
break;
case 2:
stop_bits = STOP_BITS_1_5;
LOG("stop bit: 1.5 bits\n");
break;
case 3:
stop_bits = STOP_BITS_2;
LOG("stop bit: 2 bits\n");
break;
}
set_data_frame(1, data_bits_count, parity, stop_bits);
receive_register_reset();
switch (data & 0x03)
{
case 1: m_br_factor = 1; break;
case 2: m_br_factor = 16; break;
case 3: m_br_factor = 64; break;
}
m_txc_count = 0;
#if 0
/* data bits */
m_receive_char_length = (((data >> 2) & 0x03) + 5);
if (BIT(data, 4))
{
/* parity */
m_receive_char_length++;
}
/* stop bits */
m_receive_char_length++;
m_receive_flags &= ~I8251_TRANSFER_RECEIVE_SYNCHRONISED;
m_receive_flags |= I8251_TRANSFER_RECEIVE_WAITING_FOR_START_BIT;
#endif
/* not expecting mode byte now */
m_flags &= ~I8251_EXPECTING_MODE;
// m_status = I8251_STATUS_TX_EMPTY | I8251_STATUS_TX_READY;
}
else
{
/* bit 7: Number of sync characters
0 = 1 character
1 = 2 character
bit 6: Synchronous mode
0 = Internal synchronisation
1 = External synchronisation
bit 5: parity type
0 = parity odd
1 = parity even
bit 4: parity test enable
0 = disable
1 = enable
bit 3,2: character length
0 = 5 bits
1 = 6 bits
2 = 7 bits
3 = 8 bits
bit 1,0 = 0
*/
LOG("I8251: Synchronous operation\n");
/* setup for sync byte(s) */
m_flags |= I8251_EXPECTING_SYNC_BYTE;
m_sync_byte_offset = 0;
if (BIT(data, 7))
{
m_sync_byte_count = 1;
}
else
{
m_sync_byte_count = 2;
}
}
}
WRITE8_MEMBER(i8251_device::control_w)
{
if (m_flags & I8251_EXPECTING_MODE)
{
if (m_flags & I8251_EXPECTING_SYNC_BYTE)
{
LOG("I8251: Sync byte\n");
LOG("Sync byte: %02x\n", data);
/* store sync byte written */
m_sync_bytes[m_sync_byte_offset] = data;
m_sync_byte_offset++;
if (m_sync_byte_offset == m_sync_byte_count)
{
/* finished transfering sync bytes, now expecting command */
m_flags &= ~(I8251_EXPECTING_MODE | I8251_EXPECTING_SYNC_BYTE);
m_sync_byte_offset = 0;
// m_status = I8251_STATUS_TX_EMPTY | I8251_STATUS_TX_READY;
}
}
else
{
mode_w(data);
}
}
else
{
command_w(data);
}
}
/*-------------------------------------------------
status_r
-------------------------------------------------*/
READ8_MEMBER(i8251_device::status_r)
{
uint8_t status = (m_dsr << 7) | m_status;
LOG("status: %02x\n", status);
return status;
}
/*-------------------------------------------------
data_w
-------------------------------------------------*/
WRITE8_MEMBER(i8251_device::data_w)
{
m_tx_data = data;
LOG("data_w %02x\n" , data);
/* writing clears */
m_status &=~I8251_STATUS_TX_READY;
update_tx_ready();
// Store state of tx enable when writing to DB buffer
if (is_tx_enabled()) {
m_flags |= I8251_DELAYED_TX_EN;
} else {
m_flags &= ~I8251_DELAYED_TX_EN;
}
check_for_tx_start();
/* if transmitter is active, then tx empty will be signalled */
update_tx_ready();
update_tx_empty();
}
/*-------------------------------------------------
receive_character - called when last
bit of data has been received
-------------------------------------------------*/
void i8251_device::receive_character(uint8_t ch)
{
LOG("receive_character %02x\n", ch);
m_rx_data = ch;
/* char has not been read and another has arrived! */
if (m_status & I8251_STATUS_RX_READY)
m_status |= I8251_STATUS_OVERRUN_ERROR;
m_status |= I8251_STATUS_RX_READY;
update_rx_ready();
}
/*-------------------------------------------------
data_r - read data
-------------------------------------------------*/
READ8_MEMBER(i8251_device::data_r)
{
LOG("read data: %02x, STATUS=%02x\n",m_rx_data,m_status);
/* reading clears */
m_status &= ~I8251_STATUS_RX_READY;
update_rx_ready();
return m_rx_data;
}
WRITE_LINE_MEMBER(i8251_device::write_rxd)
{
m_rxd = state;
// device_serial_interface::rx_w(state);
}
WRITE_LINE_MEMBER(i8251_device::write_cts)
{
m_cts = state;
check_for_tx_start();
update_tx_ready();
update_tx_empty();
}
WRITE_LINE_MEMBER(i8251_device::write_dsr)
{
m_dsr = !state;
}
WRITE_LINE_MEMBER(i8251_device::write_rxc)
{
if (m_rxc != state)
{
m_rxc = state;
if (m_rxc)
receive_clock();
}
}
WRITE_LINE_MEMBER(i8251_device::write_txc)
{
if (m_txc != state)
{
m_txc = state;
if (!m_txc)
transmit_clock();
}
}
READ_LINE_MEMBER(i8251_device::txrdy_r)
{
return is_tx_enabled() && (m_status & I8251_STATUS_TX_READY) != 0;
}
WRITE8_MEMBER(v53_scu_device::command_w)
{
i8251_device::command_w(data);
}
WRITE8_MEMBER(v53_scu_device::mode_w)
{
i8251_device::mode_w(data);
}